United States Court of Appeals
                     For the First Circuit


No. 23-1391

 TYNGSBORO SPORTS II SOLAR, LLC and 201 OAK PEMBROKE SOLAR LLC,
  individually and on behalf of all others similarly situated,

                     Plaintiffs, Appellants,

                               v.

   NATIONAL GRID USA SERVICE COMPANY, INC. and MASSACHUSETTS
                       ELECTRIC COMPANY,

                     Defendants, Appellees.


          APPEAL FROM THE UNITED STATES DISTRICT COURT
               FOR THE DISTRICT OF MASSACHUSETTS

         [Hon. Richard G. Stearns, U.S. District Judge]


                             Before

                  Rikelman, Selya, and Howard,
                        Circuit Judges.


          Andrew M. McNeela, with whom John R. Low-Beer, David E.
Kovel, Kirby McInerney LLP, Seth H. Handy, and Handy Law LLC were
on brief, for appellants.
          Richard H. Brown, with whom Michael J. Fitzpatrick and
Day Pitney LLP were on brief, for appellees.


                        December 6, 2023
           HOWARD, Circuit Judge.          For the past nine years, various

renewable-energy generators have unsuccessfully petitioned state

authorities   to    prohibit     utility    companies   from   charging     them

certain tax-related fees. Seeking better fortune in federal court,

two such generators brought this putative class action, but the

district court dismissed the case after finding that it lacked

subject-matter jurisdiction.         The generators now appeal, arguing

that the court had jurisdiction based on the suit's connection to

federal tax law.         Yet their complaint does not bring any claim

that arises under federal law.           Accordingly, we affirm.

                                I. BACKGROUND

                                A. The Parties

           The fees at issue are features of service agreements

between Tyngsboro Sports II Solar, LLC and 201 Oak Pembroke Solar

LLC   (collectively,      the   "Solar   Companies"     or   "Companies")   and

National   Grid    USA    Service   Company    and   Massachusetts   Electric

Company (collectively, "National Grid").1             National Grid operates

an "electric distribution network" -- a system that delivers

electricity from a "transmission network" to customers.2 The Solar

Companies operate solar-generation projects in Massachusetts.


      1The appellees are both subsidiaries of the same utility
conglomerate. Any distinction between the two is irrelevant to
this appeal.
      2For the purposes of this dispute, a transmission network is
critically different from a distribution network.     Transmission
networks operate at a very high voltage and move electricity from
                                     - 2 -
           To     deliver         solar-generated      electricity        to     their

Massachusetts-based customers, the Solar Companies need to connect

to   National     Grid's    distribution       network,       and    to   make   this

connection, National Grid must modify its hardware.                   National Grid

charges the Companies for the right to use the distribution network

and for the costs of the modifications.                 These arrangements are

governed     in   part      by     standardized       interconnection          service

agreements (ISAs) between National Grid and each Company.                          The

ISAs are at the heart of a long-running dispute between the Solar

Companies and National Grid, specifically, their requirement that

the Solar Companies pay a "tax gross up" that compensates National

Grid for any tax liability incurred by the transaction.

                                   B. The Dispute

           National        Grid     contends   that     the    Solar      Companies'

interconnection payments are taxable income to it and therefore

the Companies must pay National Grid a tax gross up to offset the

liability.      The