A Kentucky clerk is being sued by four couples – two heterosexual and two homosexual – for refusing to issue any marriage licenses since the US Supreme Court legalised gay marriage last week.

The American Civil Liberties Union of Kentucky filed a lawsuit against Rowan County clerk Kim Davis on Thursday afternoon on behalf of the couples.

Defending her decision earlier this week, Davis told the Associated Press: "It's a deep-rooted conviction; my conscience won't allow me to do that. It goes against everything I hold dear, everything sacred in my life."

She said she came to the decision after a time of prayer and fasting, according to local news site Lex18.

Shortly after the Supreme Court's decision was announced, Kentucky Governor Steve Beshear said: "While there are certainly strongly held views on both sides of this issue, the fact remains that each clerk vowed to uphold the law regardless of his or her personal beliefs. I appreciate the clerks who are fulfilling their duties, issuing licenses to all couples, and I would expect others to execute the duties of their offices as prescribed by law and to issue marriage licenses to all Kentuckians."

The lawsuit calls for an injunction to order Davis to begin issuing licenses, alleging that her refusal is "unconstitutional". 

"When our laws are updated or changed, government officials have a duty and a responsibility to impartially administer those laws," said ACLU of Kentucky executive director Michael Aldridge in a statement.

But Davis is not alone in refusing to issue licenses. In Texas, Hood county clerk Katie Lang has also declined a same-sex marriage license, and, according to local news reports, she may also face a lawsuit.

Jim Cato, who is applying for a gay marriage license, told abc-affiliate WFAA yesterday that they would make one more attempt to contact her before taking legal action. "They're sending Miss Lang a letter today. If she does not issue a license immediately, we'll move forward with the suit," he said.

Although the issue hasn't yet presented a problem in South Dakota, state attorney general Marty Jackley said yesterday that the right for same-sex couples to marry must coexist with county employees' right to marry.

He added that the "commonsense solution" would be for another county employee to issue the license, or an official from another county. However, the four couples in Rowan County have said they wish to obtain a marriage license in their home county, where they live and work.