By Cherri Gregg

PHILADELPHIA (CBS) — Same-sex marriage advocates filed a federal lawsuit this week challenging Pennsylvania’s “Defense of Marriage Act” (DOMA).

The case attacks the Commonwealth’s refusal to recognize gay marriages performed legally in other states.

The suit for the first time raises questions about the “full faith and credit” clause of the US Constitution, which requires states to respect the judgments and orders of other states.

Plaintiffs Cara Palladino and Isabelle Barker were legally married in Massachusetts, but under Pennsylvania’s DOMA their marriage is void.

“Pennsylvania and the other states by tradition not only accept the marriages of other states, but also the marriages in other countries,” notes Malcolm Lazin, executive director of Equality Forum, which organized the lawsuit.

Lazin says equal protection, due process, and full faith and credit all prohibit Pennsylvania from forcing gay couples married in other states to pay more taxes than heterosexual couples married elsewhere.

“It just creates a real inequality that makes life very difficult and is really contrary to what marital laws are supposed to do, which is to enhance family values,” Lazin tells KYW Newsradio.

This case is one of several currently pending in challenge to Pennsylvania’s DOMA.