PORTLAND (KTVB) -- U.S. District Judge Michael McShane has ruled that Oregon's voter-approved ban on gay marriage is unconstitutional.

Officials in Oregon's largest county, Multnomah, began issuing marriage licenses immediately.

“Marriage equality is about fairness. It’s about justice. It’s about caring,” Ore. Senate President Peter Courtney said.

Late Monday morning, an appeals court denied a request for an emergency stay that could have blocked McShane's ruling.

The state attorney general had refused to defend the ban in lawsuits brought by four same-sex couples.

"Today Judge McShane did the right thing for families, affirming that the denial of marriage to committed same-sex couples in Oregon is unconstitutional. In recognition of the strong support for marriage among Oregonians, no one with legal standing, including our state Attorney General, wanted to go down in history as defending discrimination," said Thalia Zepatos, director of public engagement at Freedom to Marry.

Four gay and lesbian couples brought the Oregon cases, arguing the state's marriage laws unconstitutionally discriminate against them and exclude them from a fundamental right to marriage.

Last week, McShane denied the National Organization for Marriage's request to intervene in a lawsuit challenging the constitutionality of Oregon’s gay marriage ban after the state’s attorney general refused to defend the public in the case.

In February, Oregon Attorney General Ellen Rosenblum said she would not defend the state against the federal suit, saying that the state’s ban was indefensible.

Gay rights groups previously said they've collected enough signatures to force a statewide vote on gay marriage in November. But they said they would discard the signatures and drop their campaign if the court rules in their favor by May 23.

The Supreme Court last year struck down the 1996 Defense of Marriage Act, which barred the federal government from recognizing same-sex marriage. It determined the law improperly deprived gay couples of due process.

Federal or state judges in Idaho, Oklahoma, Virginia, Michigan, Texas, Utah and Arkansas recently have found state same-sex marriage bans to be unconstitutional. Judges also have ordered Kentucky, Ohio and Tennessee to recognize same-sex marriages from other states.

But opposition remains stiff in many places. Critics note most states still do not allow gay marriage and that in most of those that do, it was the work of courts or legislatures, not the will of the people.

Oregon law has long prohibited same-sex marriage, and voters added the ban to the state constitution in 2004. The decision, approved by 57 percent of voters, came months after Multnomah County briefly issued marriage licenses to same-sex couples.

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