The brief, filed Friday, supports the challenge that the 1996 act's definition of marriage as between a man and a woman for the purposes of federal law is unconstitutional because it excludes same-sex couples from all marriage-based federal responsibilities and rights, Democratic leadership said in a release.
Forty Senate members and 172 House members are signatories on the amicus brief.
The leadership said the congressional members wanted to file the brief because they "want the Supreme Court to hear the full story from Congress and to explain why they believe that Section 3 of DOMA is unconstitutional."
The amicus brief filed also makes it clear "many members believe that Section 3 [which defines marriage] should be struck down because there simply is no legitimate federal interest in denying married same-sex couples the legal security, rights and responsibilities that federal law provides to all other married couples."
The Supreme Court is hearing a challenge to a 2nd U.S. Circuit Court of Appeals ruling that DOMA violated the Fifth Amendment's equal protection guarantee.
The members' brief urged the Supreme Court to uphold the appeal court decision.
When DOMA was passed, same-sex marriage was illegal. Now, same-sex marriage is legal in nine states and the District of Columbia.
"Virtually every aspect of DOMA and its legislative history -- the lack of objective, rational fact-finding to connect the exclusion of married same-sex couples to a legitimate federal interest; the sweeping exclusion of gay men and lesbians based on a single identifiable trait; and the open desire of some to express disapproval of that minority group -- distinguishes it from routine acts of Congress," the brief said. "None of the arguments advanced in its defense is sufficient."
"DOMA imposes a sweeping and unjustifiable federal disability on married same-sex couples," the brief said in its conclusion.
The brief was silent on the Supreme Court challenge of Proposition 8, which bans same-sex marriage in California.
The Obama administration filed a friend-of-the-court brief in the Prop. 8 challenge, saying California's ban on same-sex marriage is unconstitutional because it violates the U.S. Constitution's guarantee of equal protection.
During a news conference Friday, President Obama said the brief advances "the basic principle, which applies to all equal protection cases. Whenever a particular group is being discriminated against, the court asks the question, 'What's the rationale for this -- and it better be a good reason. And if you don't have a good reason, we're going to strike it down.'"
Obama said same-sex couples constitute a class that deserves heightened scrutiny.
"The basic principle, though, is let's treat everybody fairly and let's treat everybody equally," Obama said. "I think that the brief that's been presented accurately reflects our views."
Justices hear arguments on the Prop. 8 challenge Tuesday and on the DOMA case Wednesday.
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