TULSA, Okla. —  Two lesbian couples filed a federal lawsuit that challenges a new state constitutional amendment banning same-sex marriage (search) as well as a related federal law.

Oklahoma (search) was one of 11 states that approved constitutional bans on gay marriage Tuesday.

The federal lawsuit filed Wednesday says the state ban violates the equal protection and due process rights of the plaintiffs by not allowing them to marry and by not recognizing civil unions performed elsewhere.

The lawsuit also challenges the federal Defense of Marriage Act (search), which permits states to ignore gay weddings performed in other states.

The plaintiffs are Mary Bishop and Sharon Baldwin of Broken Arrow, who have lived together for eight years, and Susan G. Barton and Gay E. Phillips of Tulsa, who were joined in a civil union in Vermont in 2001.

The other states that approved such amendments Tuesday were Oregon, Arkansas, Georgia, Kentucky, Michigan, Mississippi, Montana, North Dakota, Ohio and Utah.