Kirkland & Ellis partner Paul Clement filed a lawsuit Tuesday against the Washington, D.C., public transportation system challenging its refusal to allow the Archdiocese of Washington to purchase and run a Christmas advertisement.

The lawsuit was filed against the Washington Metropolitan Area Transit Authority, regionally known as Metro, and its general manager, Paul Wiedefeld, in the U.S. District Court for the District of Columbia. The complaint alleges that by denying the archdiocese's request to purchase advertising space on public buses, Metro is violating its First Amendment rights.

“The First Amendment, with its guarantees of free speech and the free exercise of religion, prevents the government from denying speech on the unreasonable, arbitrary and discriminatory grounds put forward by WMATA,” Clement, the former solicitor general, wrote in the complaint.

Sherri Ly, a spokeswoman for WMATA, said the ad was declined “because it is prohibited by WMATA's current advertising guidelines.” The transportation system is represented by Rex Heinke and Tony Pierce of Akin Gump Strauss Hauer & Feld.

It's not the first time Metro has been sued over its advertising policy. The American Civil Liberties Union teamed up with conservative commentator Milo Yiannopoulos to sue the system on similar grounds in August over refusing to accept ads for his book. The case is still pending, but Metro argues that a 2015 change to its advertising rules prohibits any issue-oriented ads, including political, religious and advocacy ads.

The ad in question in the archdiocese's lawsuit relates to the group's “Find the Perfect Gift” advertising campaign, the goal of which is to “encourage individuals to seek spiritual gifts during this Christmas season,” the complaint said. The ads generally feature a starry night with silhouettes of shepherds and sheep on a hill, and a referral to the internet website FindThePerfectGift.org.

The complaint said that when the archdiocese inquired about purchasing ad space, a representative of WMATA's third-party vendor that handles ads said the campaign would not be in compliance with Metro's rules. The complaint also alleges WMATA ignored requests from the archdiocese to meet with Metro's general counsel.

The lawsuit claims there are no formal regulations or guidance on what speech is forbidden under Metro's rules. Because the discretion on what ads are banned is left to WMATA and its general manager, the lawsuit claims, the ban is applied in a way that is “arbitrary and unreasonable.”

“To borrow from a favorite Christmas story, under WMATA's guidelines, if the ads are about packages, boxes or bags … if Christmas comes from a store … then it seems WMATA approves. But if Christmas means a little bit more, WMATA plays Grinch,” the archdiocese's secretary for communications, Ed McFadden, said in a statement.

Other Kirkland lawyers on Clement's team include Mike Williams, Megan Wold, Kasdin Mitchell and Joseph Schroeder.

Correction: This story has been updated to correct the names of the Akin Gump attorneys representing WMATA.