State Attorney General Martha Coakley filed the lawsuit Wednesday in federal court in Boston. It says the federal Defense of Marriage Act interferes with the right of Massachusetts to define marriage as it sees fit.
The 1996 federal law denies federal recognition of gay marriage. Massachusetts was the first state to allow the practice.
The Boston-based Gay & Lesbian Advocates & Defenders has already sued over the federal law. It says it discriminates against gay couples and is unconstitutional because it denies them access to federal benefits that other married couples receive.