Supporters of same-sex marriage hold photos of themselves and their family members or partners on the steps of the Wayne L Morse U.S. Courthouse Wednesday, May 14, 2014, in Eugene, Ore. A federal judge will hear arguments Wednesday about whether a national group can defend Oregon's ban on same-sex marriage because the state's attorney general has refused to do so. Photo: Chris Pietsch, The Register-Guard (AP)

Supporters of same-sex marriage hold photos of themselves and their family members or partners on the steps of the Wayne L Morse U.S. Courthouse Wednesday, May 14, 2014, in Eugene, Ore. A federal judge will hear arguments Wednesday about whether a national group can defend Oregon's ban on same-sex marriage because the state's attorney general has refused to do so. Photo: Chris Pietsch, The Register-Guard (AP)

PORTLAND, Ore. — A federal judge says he’ll issue a decision next week on a constitutional challenge to Oregon’s same-sex marriage ban.

U.S. District Judge Michael McShane has notified attorneys that he’ll publish his decision at noon Monday.

Four gay and lesbian couples brought suit arguing Oregon’s marriage laws unconstitutionally discriminate against same-sex couples. Democratic Attorney General Ellen Rosenblum said the ban is legally indefensible and refused to offer arguments supporting it.

State officials have said same-sex marriages could begin almost immediately after a decision.

McShane heard arguments on the case in April, and rejected an attempt by the National Organization for Marriage to intervene.

The group argued it should be allowed to defend the ban on behalf of its Oregon members after the attorney general’s decision. But McShane said the attorney general is accountable to Oregon voters, not a third party.

Federal judges in seven states have thrown out voter-approved bans on same-sex marriage on constitutional grounds since the U.S. Supreme Court struck down a portion of the federal Defense of Marriage Act last year. More challenges are pending.

The most recent was Tuesday, when U.S. District Magistrate Judge Candy Dale overturned Idaho’s same-sex marriage ban. On Thursday, a federal appeals court placed her ruling temporarily on hold while it decides whether to issue a lengthier stay for appeals by Idaho’s governor and attorney general.

In Oregon, Portland attorneys Lake Perriguey and Lea Ann Easton filed a lawsuit in October on behalf of two women in a relationship for more than 30 years. Two months later, the American Civil Liberties Union and lawyers from two firms went to court on behalf of a lesbian couple and a gay couple.

Oregon law has long prohibited same-sex marriage. Its ban, approved by 57 percent of voters, came months after Multnomah County briefly issued marriage licenses to same-sex couples. Multnomah includes Portland and is the state’s largest county.

About 3,000 gay couples were allowed to marry before a judge halted the practice. The Oregon Supreme Court later invalidated the marriages.

Advocacy groups say they have collected enough signatures to ask voters in November whether same-sex marriage should be legal. They have said they would discard the signatures if the judge rules in their favor. The group has until July 3 to submit just over 116,000 valid signatures.