Oregon Attorney General Ellen Rosenblum announced Thursday that she won't defend the state's gay marriage ban in court.

The ban “cannot withstand a federal constitutional challenge under any standard of review,” Rosenblum said in a court filing.

Rosenblum is the sixth Democratic attorney general to refuse to defend such laws, joining Kamala Harris of California, Mark Herring of Virginia, Lisa Madigan of Illinois, Kathleen Kane of Pennsylvania and Catherine Cortez Masto of Nevada. Masto recently withdrew a court filing in which she defended Nevada's ban.

(Related: Nevada withdraws defense of gay marriage ban that invoked bigamy, incest.)

In January, a federal judge consolidated two lawsuits challenging the constitutionality of Oregon's 2004 voter-approved constitutional amendment limiting marriage to heterosexual couples.

A petition drive to repeal the ban is being spearheaded by the group Oregon United for Marriage. If successful, Oregon would make history as the first state to repeal such a ban.

Oregon currently recognizes the out-of-state legal marriages of gay couples.