By Laura Zuckerman
May 21 (Reuters) - Four Montana couples asked a federal judge on Wednesday to overturn a state constitutional amendment prohibiting gay marriage, the latest challenge to bans on same-sex matrimony that have been struck down by a string of U.S. courts.
The lawsuit brought by four gay and lesbian couples alleges that Montana's voter-approved ban unfairly denies them protections such as job benefits and joint adoption afforded to heterosexual couples under state and federal laws.
The Montana action came the same day the governor of Pennsylvania said he would not challenge a judge's ruling on Tuesday that struck down its own ban on gay marriage, making it the 19th state to gain legal standing for same-sex nuptials.
Another U.S. district judge declared a similar ban on gay marriage unconstitutional in Oregon on Monday.
Legal challenges have been brought against constitutional bans on same-sex matrimony in 27 of the 29 states where voters approved amendments defining marriage as between a man and a woman, said James Esseks, director of the ACLU's Lesbian Gay Bisexual Transgender Project.
No lawsuits have yet sought to overturn constitutional bans in North Dakota and South Dakota, but a case is anticipated shortly in South Dakota, he said.
Lawsuits contesting bans on gay marriage have seen them overturned but later stayed pending appeals in 11 states, including Texas, Virginia and Idaho. The efforts have gained traction since a U.S. Supreme Court decision in June found that married gay couples were eligible for federal benefits.
Montana Attorney General Tim Fox, a Republican and a defendant in the lawsuit brought by the Montana ACLU on behalf of the four gay couples, did not immediately respond to a question about whether he will defend the state ban.
But Montana's Democratic Governor Steve Bullock hailed the legal action.
"Montanans cherish our freedom and recognize the individual dignity of every one of us. The time has come for our state to recognize and celebrate - not discriminate against - two people who love one another, are committed to each other and want to spend their lives together," he said in a statement.
Bullock is not named in the lawsuit. (Editing by Cynthia Johnston and Gunna Dickson)