A male gay couple has filed a federal lawsuit challenging Virginia's 2006 voter-approved constitutional amendment which defines marriage as a heterosexual union.

The amendment, known as the Marshall-Newman Amendment after its authors Delegate Bob Marshall and Senator Steve Newman, also prohibits the state from recognizing gay and lesbian couples with civil unions or domestic partnerships.

The gay couple together 25 years - Timothy B. Bostic, a professor at Old Dominion University, and Tony C. London, a successful realtor from Norfolk – argue in their suit filed last week that the state of Virginia is violating their Fourteenth Amendment rights to due process and equal protection by denying them the right to marry.

“The disadvantage these laws impose upon gays and lesbians is the result of disapproval or animus against a politically unpopular group,” lawyers representing the plaintiffs wrote. “Accordingly, these laws violate the Equal Protection Clause of the Fourteenth Amendment to the United States Constitution by casting gays and lesbians into disfavored legal status and categorizing them as 'second-class' citizens.”

The lawsuit is part of a rash of legal filings filed in multiple states soon after the Supreme Court eviscerated the heart of the Defense of Marriage Act (DOMA) in June. The high court ruled unconstitutional DOMA's provision prohibiting federal agencies from recognizing the legal marriages of gay couples.

In most, if not all, of the cases filed in its wake, plaintiffs are using the decision to support their claims.

Recent decisions in Ohio and Michigan were won using the high court's DOMA decision.

The ACLU and Lambda Legal have also announced plans to file a lawsuit challenging Virginia's marriage ban.