Four gay couples in Louisiana on Wednesday filed a federal lawsuit challenging the constitutionality of Louisiana's ban on recognizing the out-of-state marriages of gay couples.

The plaintiff couples – one of which is lesbian – are represented by the New Orleans law firm of Stone Pigman Walter Wittmann on behalf of Forum for Equality Louisiana, an LGBT rights group.

The plaintiffs claim that Louisiana singles out only gay couples for unequal treatment, a violation of the constitutional guarantees of equal protection and due process.

“Louisiana's disparate treatment of same-sex and opposite-sex couples who are married outside of Louisiana demonstrates that the purpose of the Louisiana Anti-Recognition Laws is to 'impose a disadvantage, a separate status, and so a stigma upon all who enter into same-sex marriages' that were lawfully celebrated in other states,” according to the lawsuit.

“This is as basic as the Golden Rule,” SaraJane Brady, executive director of Forum for Equality Louisiana, said in an emailed statement. “Treating others as one would want to be treated includes extending all the rights and privileges of marriage to lesbian and gay couples who are truly committed to each other. This lawsuit would uphold this very basic principle of freedom for all Louisianans.”

An overwhelming majority (78%) of voters approved Louisiana's 2004 constitutional amendment which states that marriage “shall consist only of the union of one man and one woman” and prohibits state officials and judges from recognizing the out-of-state marriages of gay couples.

The Louisiana Supreme Court upheld the amendment in 2005.