The plaintiffs want the state's Defense of Marriage Act declared unconstitutional, the Pittsburgh Post-Gazette reported.
The American Civil Liberties Union and a Philadelphia law firm filed the lawsuit in federal court in Harrisburg on behalf of the plaintiffs.
Witold Walczak, legal director of the Pennsylvania ACLU, said he hopes the suit will establish the "legitimacy" of same-sex marriage in the state.
Walczak said he expected the suit to go to trial.
The U.S. Supreme Court two weeks ago struck down the federal Defense of Marriage Act in a 5-4 vote. In its decision, the court did not spell out if a constitutional right to marriage existed. It also did not invalidate state laws that ban gay marriage.
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