 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued April 16, 2019                  Decided June 11, 2019

                        No. 18-1195

    AMERICAN FEDERATION OF GOVERNMENT EMPLOYEES
             NATIONAL COUNCIL, 118-ICE,
                     PETITIONER

                              v.

          FEDERAL LABOR RELATIONS AUTHORITY,
                     RESPONDENT

   UNITED STATES DEPARTMENT OF HOMELAND SECURITY,
       IMMIGRATION AND CUSTOMS ENFORCEMENT,
                     INTERVENOR


          On Petition for Review of a Final Order
          of the Federal Labor Relations Authority


     T. Reid Coploff argued the cause and filed briefs for the
petitioner.

    Tabitha G. Macko, Attorney, Federal Labor Relations
Authority, argued the cause for the respondent. Rebecca J.
Osborne, Acting Deputy Solicitor, was with her on brief.

     Joseph F. Busa, Attorney, United States Department of
Justice, argued the cause for the intervenor. H. Thomas Byron
III, Attorney, and Mark A. Robbins, General Counsel, United
                             2
States Office of Personnel Management, were with him on
brief.

    Before: HENDERSON, PILLARD and WILKINS, Circuit
Judges.

    Opinion for the Court filed by Circuit Judge HENDERSON.

     KAREN LECRAFT HENDERSON, Circuit Judge: At the
urging of the Office of Special Counsel and the Government
Accountability Office, the Department of Homeland Security,
Immigration and Customs Enforcement (ICE) changed how it
calculates overtime pay for certain employees. Concerned by
the potential drop in its members’ overtime pay, the American
Federation of Government Employees National Council, 118-
ICE (Union) representing ICE employees filed a grievance
against ICE for changing its policy without first bargaining.
The Federal Labor Relations Authority (Authority), however,
determined that ICE had no duty to bargain with the Union
before changing its overtime policy because ICE’s previous
policy was unlawful. In re U.S. Dep’t of Homeland Sec. U.S.
Immigration & Customs Enf’t (In re ICE), 70 F.L.R.A. 628,
630 (2018). We agree with the Authority and therefore deny
the Union’s petition for review.

                     I. BACKGROUND

    Federal law governing overtime pay generally requires a
federal employee to obtain administrative approval before
working over eight hours in one day or forty hours in one
workweek. 5 U.S.C. § 5542(a); 5 C.F.R. § 550.111(a)(1).
Some federal employees, such as law enforcement personnel,
however, hold positions “in which the hours of duty cannot be
controlled administratively” because the employees must work
“substantial amounts of irregular, unscheduled overtime.” 5
U.S.C. § 5545(c)(2). To compensate federal employees for
                               3
this “Administratively Uncontrollable Overtime” or “AUO,”
the Congress authorized agencies to provide a special
“premium pay” equal to “an appropriate percentage, not less
than 10 percent nor more than 25 percent, of the rate of basic
pay for the position, as determined by taking into consideration
the frequency and duration of irregular, unscheduled overtime
duty required in the position.” Id.

    The Congress delegated to the Office of Personnel
Management (OPM) the authority to promulgate regulations
governing the calculation of AUO premium payments. 5
U.S.C. § 5548(a). In 1968, the OPM adopted a policy under
which the amount of the premium payment turns on the average
number of AUO hours an eligible employee works per week.
See Revision of Regulations, 33 Fed. Reg. 12,402, 12,462–64
(Sept. 4, 1968) (codified as amended at 5 C.F.R. §§ 550.151–
550.164). Eligible employees receive a premium payment
based on the following table:

                                           Premium Payment
         Average Weekly AUO                 (As a Percentage
                                              of Base Pay)
  At least 3 but not more than 5 hours            10%
 More than 5 but not more than 7 hours            15%
 More than 7 but not more than 9 hours            20%
           More than 9 hours                      25%


See 5 C.F.R. § 550.154(a). An agency must review its
employees’ average weekly AUO “at appropriate intervals.”
Id. § 550.161(f). If an employee’s average changes during the
applicable review period, the agency must “discontinu[e]
payments or revis[e] rates of premium pay” as necessary. Id.

   Although the OPM’s regulations linked AUO premium
payments to an employee’s average weekly AUO, the
                               4
regulations did not originally specify how to account for leave
time in that calculation. See id. §§ 550.153–550.162. How
an agency accounts for leave time, however, can directly affect
an employee’s premium payments. That is, if an agency
counts leave time toward the length of the applicable review
period, an employee’s average weekly AUO and corresponding
premium payment can drop.

     To illustrate, an employee accumulating 72 hours of AUO
over a 12-week review period would average 6 hours of AUO
per week and therefore would receive a premium payment
equal to 15% of his base pay rate. But if the same employee
maintains his 6-hours-per-week average for ten weeks and
takes two weeks of leave during which he accumulates no
AUO, a total of 60 hours of AUO accumulates. If the agency
does not exclude the two weeks of leave, the employee would
see his average weekly AUO for the 12-week review period fall
to 5 hours per week and his premium payment drop to 10%.
On the other hand, if the agency excludes the two weeks, the
employee’s average weekly AUO for the now-reduced 10-
week review period would remain at 6 hours per week and his
premium payment would hold steady at 15%.

     To resolve any uncertainty under its regulations, the OPM
issued a guidance in 1997 instructing all federal agencies not
to exclude leave time from their calculation of average weekly
AUO. See Attachment to Memorandum from Steven R.
Cohen, Acting Assoc. Dir. for Human Res. Sys., OPM, to Dirs.
of Personnel, Guidance on AUO Pay (CPM 97-5) (June 13,
1997) (hereinafter “1997 Guidance”). Specifically, the 1997
Guidance clarified that “in determining the number of weeks in
a review period,” agencies should not “reduce the number of
weeks by subtracting,” inter alia, “hours of paid leave (such as
annual leave or sick leave)” or “hours of unpaid leave (such as
hours of leave without pay, including leave without pay under
                                 5
the Family and Medical Leave Act of 1993 (FMLA), or hours
during which an employee is suspended without pay).” 1997
Guidance at 4. 1

     Despite the OPM’s 1997 Guidance, ICE—following the
lead of the Immigration and Naturalization Service, its
predecessor—continued to exclude leave time such as military
leave, annual leave and sick leave from its AUO calculations.
ICE’s AUO policy remained unaddressed for over a decade but
government oversight agencies eventually began to take notice.
In 2013 the Office of Special Counsel, acting pursuant to its
authority under the Whistleblower Protection Act, 5 U.S.C.
§§ 1211–1219, warned the Congress that the Department of
Homeland Security (DHS) and its components such as ICE
were abusing AUO premium pay. See Abuse of Overtime at
DHS: Padding Paychecks and Pensions at Taxpayer Expense:
Hearing Before the H. Comm. on Oversight & Gov’t Reform,
113th Cong. 14–22 (2013) (statement of Carolyn N. Lerner,
Special Counsel, U.S. Office of Special Counsel). A year
later, the Government Accountability Office reported that ICE
administered AUO premium payments contrary to governing
rules by, for example, continuing to “provide for excludable
days during periods of leave including annual or sick leave, or
for periods of leave without pay . . . [n]otwithstanding OPM’s
1997 guidance.” U.S. Gov’t Accountability Office, GAO-15-
95, Department of Homeland Security: Continued Action
Needed to Strengthen Management of Administratively

    1
       After the emergency response to the terrorist attacks on
September 11, 2001, the OPM added three exceptions to its general
no-exclusion policy: (1) temporary assignments that are not eligible
for AUO, (2) temporary assignments for advanced training duty and
(3) temporary assignments that are “directly related to a national
emergency.” Administratively Uncontrollable Overtime Pay, 67
Fed. Reg. 6640, 6641 (Feb. 13, 2002) (codified as amended at 5
C.F.R. §§ 550.154(c), 550.162(g)); see 5 C.F.R. § 550.162(c).
                               6
Uncontrollable Overtime 27 (2014). The DHS responded by
informing its components that it was “ending the practice of
using excludable days in a manner that is inconsistent with the
governing regulations” and instructing them to “take
immediate action to correct these ongoing and unauthorized
practices.”   Memorandum from Chip Fulghum, Acting
Deputy Under Sec’y for Mgmt., DHS, to Component Heads,
Component Plans to Improve the Administration of
Administratively Uncontrollable Overtime (AUO) in the
Department of Homeland Security 2 (Jan. 7, 2015).

     On May 2, 2015, ICE complied with the DHS’s
instructions and ended its policy of excluding leave time from
its calculation of average weekly AUO. Email from Daniel
Ragsdale, Deputy Dir., ICE, to all ICE Employees, Changes in
Calculations of Administratively Uncontrollable Overtime
(AUO) (May 2, 2015). ICE then notified its employees’
Union and offered to engage in post-implementation
bargaining regarding the change to its AUO policy.
Unsatisfied with post-implementation bargaining, the Union
filed a grievance against ICE alleging that ICE committed an
unfair labor practice under the Federal Service Labor-
Management Relations Statute (FSLMRS), 5 U.S.C. §§ 7101–
7135, by unilaterally changing its AUO policy without first
bargaining with the Union. ICE denied the grievance but an
arbitrator ruled in the Union’s favor and ordered ICE to
reinstate its previous AUO policy and to bargain with the
Union before making any future changes.

     The Authority, however, set aside the arbitrator’s award as
contrary to law. In re ICE, 70 F.L.R.A. at 628–30; see 5
U.S.C. § 7122(a)(1) (authorizing Authority to “take such
action . . . concerning the [arbitrator’s] award as it considers
necessary” if it finds award is “contrary to any law, rule, or
regulation”). The Authority determined that ICE’s previous
                               7
policy of excluding leave time from its AUO calculations was
contrary to the OPM’s regulations and the 1997 Guidance and
that ICE thus had no duty under the FSLMRS to bargain with
the Union before abandoning its unlawful practice. In re ICE,
70 F.L.R.A. at 630. The Union does not claim that ICE had
an obligation to engage in impact and implementation
bargaining before instituting the change. The Union timely
petitioned for review of the Authority’s order. See 5 U.S.C.
§ 7123(a).

                        II. ANALYSIS

     We will set aside the Authority’s order if it is “arbitrary,
capricious, an abuse of discretion, or otherwise not in
accordance with law.” Id. § 706(2)(A); see id. § 7123(c)
(“Review of the Authority’s order shall be on the record in
accordance with section 706 of this title.”). The Authority’s
order rests on two conclusions: (1) ICE’s previous AUO policy
was unlawful under the OPM’s regulations and Guidance and
(2) ICE therefore had no duty under the FSLMRS to bargain
with the Union before changing its policy. In re ICE, 70
F.L.R.A. at 630. The Union does not dispute that the second
conclusion correctly states the applicable law if the first
conclusion is substantiated. See 5 U.S.C. § 7117(a)(1)
(“[T]he duty to bargain in good faith” does not extend to
matters “inconsistent with any Federal law or any Government-
wide rule or regulation.”). Thus, whether we should set aside
the Authority’s decision turns entirely on whether it correctly
determined that ICE’s previous policy conflicted with the
OPM’s regulations as interpreted in the 1997 Guidance.

     On its face, the OPM’s 1997 Guidance expressly prohibits
ICE’s previous policy of excluding leave time from its AUO
calculations. The 1997 Guidance states that “in determining
the number of weeks in a review period, there is no authority
                                  8
to reduce the number of weeks by subtracting hours of paid
leave (such as annual leave or sick leave)” or “hours of unpaid
leave (such as hours of leave without pay, including leave
without pay under the Family and Medical Leave Act of 1993
(FMLA), or hours during which an employee is suspended
without pay).” 1997 Guidance at 4 (emphasis added). In
2002, the OPM amended its AUO regulations, creating a
limited set of exceptions from its no-excludible-days policy to
address exigencies related to the September 11, 2001 terrorist
attacks. See Administratively Uncontrollable Overtime Pay,
67 Fed. Reg. at 6640–41. The OPM’s decision that these
changes were “necessary” to keep employees temporarily
assigned to non-AUO qualifying positions from experiencing
reductions in their AUO rates, id. at 6640, confirmed the
default rule reflected in the 1997 Guidance that agencies
otherwise lack discretion to exclude days. ICE’s previous
policy of excluding leave time was therefore unlawful under a
straightforward reading of the 1997 Guidance and the 2002
amendments to the regulations. Nevertheless, the Union
makes three arguments that support its position that ICE’s
previous AUO policy was consistent with the 1997 Guidance.
None is persuasive.

     First, as a textual matter, the Union argues that the 1997
Guidance’s prohibition on excluding leave extends only to
hours of leave, preserving an agency’s discretion to exclude
days of leave. As evidence, the Union observes that, in
identifying the units of time an agency should not exclude from
its AUO calculations, the 1997 Guidance lists only “hours” of
paid and unpaid leave but lists both “days” and “hours” “during
which an employee has been detailed to other duties for which
employees seldom or never perform irregular or occasional
overtime work.” 1997 Guidance at 4–5. 2 The Union draws

    2
        The full relevant portion of the 1997 Guidance reads:
                                9
too much from too little. Both “hours” and “days” refer to
units of time that can be used interchangeably, in this case with
eight hours equaling one day. Indeed, the relevant portion of
the 1997 Guidance assumes that the units of time are
interchangeable by speaking of subtracting “hours” and “days”
from a third unit of time, “weeks.” Id. at 4. The Union,
moreover, has offered no practical reason why the OPM would
have intended an agency to treat employees who take partial
days of leave differently from those who take full days—why,
for example, an employee who calls in sick before work begins
should be able to exclude his sick time but an employee who
becomes ill at the office, leaves after lunch and takes four hours
of sick leave should not. We thus read the 1997 Guidance as
using different units of time to convey one concept: an agency
should not exclude leave or other official time, whether
measured in “hours” or “days,” in calculating its employees’
average weekly AUO.

     Second, the Union asserts that a subsequent provision of
the 1997 Guidance discussing “extended absence[s]” gives an


       [I]n determining the number of weeks in a review
       period, there is no authority to reduce the number of
       weeks by subtracting hours of paid leave (such as
       annual leave or sick leave), hours of unpaid leave
       (such as hours of leave without pay, including leave
       without pay under the Family and Medical Leave
       Act of 1993 (FMLA), or hours during which an
       employee is suspended without pay), hours of
       excused absence with pay, hours or days during
       which an employee has been detailed to other duties
       for which employees seldom or never perform
       irregular or occasional overtime work, or hours in a
       training status.

1997 Guidance at 4–5 (emphases added).
                                 10
agency some discretion in excluding leave time. See id. at 5.
The Union, however, forfeited this argument by failing to raise
it in its opening brief. See Al-Tamimi v. Adelson, 916 F.3d 1,
6 (D.C. Cir. 2019).

     Third, the Union insists that “30 years” of “settled law”
have recognized that ICE’s previous policy of excluding leave
time was lawful under the OPM regulations. But the decisions
the Union cites do not constitute authority anywhere close to
settled law. To start, the first two decisions on which the
Union relies pre-date the 1997 Guidance by more than a decade
and thus offer no assistance in determining whether ICE’s
previous policy of excluding leave time conflicts with the 1997
Guidance. See Beeunas v. United States, 1 Cl. Ct. 706 (1983);
In re Nat’l Border Patrol Council, 23 F.L.R.A. 106 (1986).
The two more recent Authority decisions the Union cites
provide it no support because the Authority subsequently
vacated both. See In re Am. Fed’n of Gov’t Emps., 70
F.L.R.A. 441 (2018) (vacating In re Am. Fed’n of Gov’t Emps.,
69 F.L.R.A. 248 (2016), and In re Am. Fed’n of Gov’t Emps.,
68 F.L.R.A. 910 (2015)). 3 In the end, the Union can point to
no relevant decisions that create “settled law” establishing that
ICE’s previous AUO policy of excluding leave time was
consistent with the 1997 Guidance.



    3
       In response, the Union argues that it is irrelevant that the
Authority vacated the two decisions because it did so for reasons
unrelated to the lawfulness of excluding leave days. The Authority
vacated the decisions pursuant to United States v. Munsingwear, Inc.,
340 U.S. 36 (1950). See In re Am. Fed’n of Gov’t Emps., 70
F.L.R.A. at 441 n.6. Munsingwear mootness is a doctrine
specifically aimed at preventing a decision subsequently mooted
“from spawning any legal consequences,” Munsingwear, 340 U.S. at
41.
                              11
    Perhaps seeing the writing on the wall, the Union belatedly
suggested at oral argument that the 1997 Guidance does not
reasonably implement the governing statute, 5 U.S.C.
§ 5545(c)(2), or the OPM regulations, 5 C.F.R. §§ 550.151–
550.164, and thus does not render ICE’s previous AUO policy
unlawful. By failing to make this argument in its briefs, the
Union forfeited the issue. See Elec. Privacy Info. Ctr. v.
Presidential Advisory Comm’n on Election Integrity, 878 F.3d
371, 379 n.6 (D.C. Cir. 2017).

     For the foregoing reasons, we deny the Union’s petition
for review.

                                                   So ordered.
