 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued February 6, 2015               Decided April 17, 2015

                        No. 14-7014

                 LOUIS P. CANNON, ET AL.,
                       APPELLANTS

                             v.

                  DISTRICT OF COLUMBIA,
                        APPELLEE


        Appeal from the United States District Court
                for the District of Columbia
                    (No. 1:12-cv-00133)


     Matthew A. LeFande argued the cause and filed the briefs
for appellants.

     Richard S. Love, Senior Assistant Attorney General,
Office of the Attorney General for the District of Columbia,
argued the cause for appellee. With him on the briefs were
Irvin B. Nathan, Attorney General, at the time the brief was
filed, Office of the Attorney General for the District of
Columbia, Todd S. Kim, Solicitor General, and Loren L.
AliKhan, Deputy Solicitor General.

    Before: KAVANAUGH, MILLETT, and WILKINS, Circuit
Judges.
                               2
   Opinion for       the   Court   filed   by   Circuit   Judge
KAVANAUGH.

     KAVANAUGH, Circuit Judge:       Plaintiffs are retired
officers of D.C.’s Metropolitan Police Department. After
retiring, they were subsequently re-hired by the D.C.
Protective Services Division, which protects government
buildings and D.C.-owned property.

    Plaintiffs received pension benefits from their service
with the Metropolitan Police Department and salaries for their
jobs with the Protective Services Division. But Section 5-
723(e) of the D.C. Code requires the D.C. Government to
reduce plaintiffs’ salaries by the amount of their pensions.
The goal of that statute is to prevent so-called double-dipping
by D.C. government employees who retire and then are re-
hired back into another D.C. government job.

     Pursuant to that statutory provision, D.C. reduced
plaintiffs’ salaries by the amount of their pensions. In
response to their salary reduction, plaintiffs sued D.C. under a
variety of theories. In an earlier round in this Court, we
considered plaintiffs’ claims under the federal Fair Labor
Standards Act, the First Amendment, the Fifth Amendment,
and the Equal Protection Clause. We ruled in favor of the
plaintiffs on the Fair Labor Standards Act claim, ruled in
favor of D.C. on the remaining constitutional claims, and
remanded for further proceedings. See Cannon v. District of
Columbia, 717 F.3d 200 (D.C. Cir. 2013).

     Plaintiffs’ victory on the FLSA claim gave them only
partial relief and did not fully restore their salaries. On
remand, still seeking to fully restore their salaries, plaintiffs
therefore filed an amended complaint that asserted a new
federal claim: that D.C.’s salary reduction provision violates
                                  3
the federal Public Salary Tax Act of 1939. See Pub. L. No.
76-32, § 4, 53 Stat. 574, 575 (1939) (codified as amended at 4
U.S.C. § 111(a)). The District Court rejected that argument,
and so do we.1

     As relevant here, the Public Salary Tax Act allows States
and D.C. to impose “taxation” on compensation paid to
employees of the Federal Government, but only so long as the
taxation does not discriminate against Federal employees as
compared to state and local government employees, for
example. 4 U.S.C. § 111(a).2 Plaintiffs’ theory here is as
follows: They say that their pensions from the D.C.
Metropolitan Police Department are actually federal
compensation (due to the complex interaction of the Federal
and D.C. Governments in funding those pensions). And they
say that D.C., by means of this salary reduction provision, is
in effect taxing plaintiffs’ federal pensions in a discriminatory
manner in violation of the Public Salary Tax Act.

     Plaintiffs’ argument under the Public Salary Tax Act has
a plethora of potential problems. One initial (and in this case
dispositive) problem with plaintiffs’ novel theory is that the

     1
       Some of the plaintiffs no longer work with the Protective
Services Division, but plaintiffs are suing for damages as well as
forward-looking injunctive relief.
     2
       The full text of the relevant provision reads: “The United
States consents to the taxation of pay or compensation for personal
service as an officer or employee of the United States, a territory or
possession or political subdivision thereof, the government of the
District of Columbia, or an agency or instrumentality of one or
more of the foregoing, by a duly constituted taxing authority having
jurisdiction, if the taxation does not discriminate against the officer
or employee because of the source of the pay or compensation.” 4
U.S.C. § 111(a).
                              4
Act applies only to “taxation.” And the D.C. salary reduction
provision at issue here is not “taxation” of plaintiffs’
pensions.

     As a general matter, taxes are a “charge,” usually
“monetary, imposed by the government on persons, entities,
transactions, or property to yield public revenue.” Black’s
Law Dictionary 1685 (10th ed. 2014). That basic definition is
longstanding. The edition of Black’s Law Dictionary in effect
when the Act was passed in 1939 defined “taxation” as an
exaction imposed by the government “for the purpose of
providing revenue for the maintenance and expenses of
government.” Black’s Law Dictionary 1707 (3d ed. 1933). A
contemporaneous edition of Webster’s concurred, defining
“taxation” as “the raising of revenue by the imposition of
compulsory contributions; also, a system of so raising
revenue.” Webster’s New International Dictionary 2587 (2d
ed. 1934). As far back as McCulloch v. Maryland, the
Supreme Court has understood the power to tax as the power
“of raising revenue, and applying it to national purposes.”
McCulloch v. Maryland, 17 U.S. 316, 409 (1819). One of the
few Supreme Court cases interpreting the Public Salary Tax
Act similarly indicates that revenue raising is a hallmark of
“taxation” under the Act. In Jefferson County v. Acker, 527
U.S. 423 (1999), the Supreme Court concluded that a license
fee imposed on judges was “revenue-raising” and constituted
taxation for purposes of the Public Salary Tax Act. Id. at 440-
42.

     Here, D.C.’s salary reduction provision is not a tax. It
does not raise revenue. Rather, it operates on the opposite
side of D.C.’s financial ledger. It reduces D.C.’s total
expenditures on salaries.       In particular, it decreases
employees’ salaries by the amount of their pensions from
prior service in the D.C. government. Moreover, the
                                5
reduction takes effect when the employee’s salary is initially
computed by the Protective Services Division. The salary
reduction is thus not collected “through the normal means of
taxation,” which is yet another indication that this is not
taxation for purposes of this Act. National Federation of
Independent Business v. Sebelius, 132 S. Ct. 2566, 2596, slip
op. at 36 (2012).

     The salary reduction statute, in short, is nothing more
than a way for D.C. to prevent so-called double-dipping and
thereby reduce its expenditures on employee salaries. It is not
a tax on plaintiffs’ pensions. We therefore reject plaintiffs’
novel Public Salary Tax Act argument.3

     In this second appeal, plaintiffs also renew the due
process and takings claims that we found unavailing on their
last trip to this Court. The law of the case doctrine bars us
from reconsidering those holdings. See PNC Financial
Services Group, Inc. v. Commissioner of IRS, 503 F.3d 119,
126 (D.C. Cir. 2007).

     Finally, plaintiffs contend that the District Court erred by
declining to exercise jurisdiction over their separate D.C. law
claims. (Plaintiffs’ complaint tacked on several D.C. law
claims to their numerous federal claims.) Plaintiffs primarily
argue that D.C. Code § 1-815.02 gives federal courts
“exclusive jurisdiction” over claims related to the payment of
their pensions. But the salary reduction provision does not
affect the amount or payment of plaintiffs’ pensions. It
affects only the amount of their salaries. See D.C. Code § 5-
723(e) (“the salary of any annuitant . . . shall be reduced by”

    3
      To be clear, we do not here purport to say what constitutes a
tax under any other statute.
                                 6
the amount “of such annuitant’s annuity”) (emphasis added).
Alternatively, plaintiffs contend that the District Court abused
its discretion by declining to exercise supplemental
jurisdiction over plaintiffs’ D.C. law claims. Federal district
courts may decline to exercise supplemental jurisdiction if,
among other things, “the claim raises a novel or complex
issue of State law.” 28 U.S.C. § 1367(c)(1). Plaintiffs’ D.C.
law claims appear to be novel. Our review of the District
Court’s declination of supplemental jurisdiction is deferential.
We conclude that the District Court did not abuse its
discretion in declining to exercise supplemental jurisdiction
over plaintiffs’ D.C. law claims.4

                               ***

    We affirm the judgment of the District Court.

                                                       So ordered.




    4
       The District Court transferred the remaining D.C. law claims
to the Superior Court. D.C. did not cross-appeal to argue that those
claims should have been dismissed rather than transferred.
Therefore, we do not consider the propriety of the transfer.
