The lawsuit, filed Tuesday, comes after the transit agency rejected Christmas ads -- to be placed on buses -- that urge worshippers to "Find the Perfect Gift."
The Archdiocese's Ed McFadden said WMATA told the Archdiocese it would not run the ad because it "depicts a religious scene and thus seeks to promote religion."
"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," McFadden said in a statement. "But if Christmas means a little bit more, WMATA plays Grinch."
WMATA, which operates the capital region's subway system and its primary bus network, defended its decision, citing its advertising guidelines in place since 2015.
"In 2015, WMATA changed its advertising policy to prohibit issue-oriented advertising, including political, religious and advocacy advertising," Metro spokeswoman Sherry Ly said in an email statement to CNN. "The ad in question was declined because it is prohibited by WMATA's current advertising guidelines."
WMATA did not provide further comment beyond the statement.
According to the lawsuit, the Archdiocese began to develop its "Find the Perfect Gift" advertising campaign in spring of 2017. The campaign was scheduled to begin on December 3 and run through the Christmas season.
Paul Clement, former Bush-era solicitor general and lawyer for the Archdiocese in this case, called WMATA's decision a violation of the First Amendment "plain and simple."
Metro is no stranger to lawsuits over its advertisement policy. In August, the American Civil Liberties Union also sued WMATA
, claiming the advertising guidelines violated free speech.
WMATA rejected "ads from four groups
that hail from across the political spectrum," the ACLU argued. This included an ACLU ad which displayed the text of the First Amendment in English, Spanish and Arabic; a Carafem ad for medication abortions; several PETA ads suggesting that people "Go Vegan"; and ads for Milo Yiannopoulos' book "Dangerous."
The ACLU lawsuit asked the court to order the agency to accept and run the ads in its trains and stations and in and on its buses. The lawsuit also asked the court to declare four sections of WMATA guidelines "unconstitutional because they violate free speech rights, are arbitrarily enforced, and are unconstitutionally vague."
The Archdiocese suit is asking for a judge to reject Metro's ad guidelines regarding religion.