A Kentucky county clerk has sued Gov. Steve Beshear on Wednesday, accusing him of violating her religious belief when he sent a letter telling all county clerks to issue licenses to same-sex couples after the US Supreme Court upheld gay marriage nationwide.

Rowan County Clerk Kim Davis, who was sued last month for refusing to issue same-sex marriage licenses, filed the lawsuit against Beshear before the US District Court in the Eastern District of Kentucky.

In her lawsuit, Davis—who was elected county clerk in November 2014 for a four-year term but served as deputy county clerk for nearly 30 years—said she has a religious belief that based on the Bible, "there is no arrangement of people other than one man and one woman that is, or can be called, 'marriage.'"

"Davis can neither authorise nor approve the 'marriage' of a same-sex couple according to her conscience, because even calling the relationship of a same-sex couple 'marriage would' violate her deeply and sincerely held religious beliefs," the lawsuit said.

She added that she believes that when she took office as county clerk last January, she swore an oath to support the US Constitution and laws which includes the phrase "so help me God." This meant "that, in upholding the federal and state constitutions and laws, she would not act in contradiction to the moral law of God, natural law, or her sincerely held religious beliefs and convictions," the lawsuit said.

It accused Beshear of issuing policies and directives that specifically target clerks like Davis who possess certain religious beliefs about marriage.

In his letter to Kentucky County Clerks last June 26, when the Supreme Court issued its historic ruling on same-sex marriage, Beshear told them that "as elected officials, each of us has taken an oath to uphold the Constitution of the United States and the Constitution of Kentucky."

"Neither your oath nor the Supreme Court dictates what you must believe. But as elected officials, they do prescribe how we must act. Effective today, Kentucky will recognise as valid all same-sex marriages performed in other states and in Kentucky," the governor said in his letter to the clerks.

A gender-neutral application for marriage license has also been issued replacing the words "bride" and "groom" with "first party" and "second party."

"While there are certainly strongly held views on both sides of this issue, I know that Kentuckians are law-abiding people and will respect the rule of law," Beshear told the county clerks.

The lawsuit against Davis was filed by the American Civil Liberties Union of Kentucky last July 2 after she refused to issue marriage licenses to same-sex couples April Miller and Karen Roberts, and L. Aaron Skaggs and Barry Spartman, and straight couples Shantel Burke and Stephen Napier and Jody Fernandez and Kevin Holloway.

ACLU attorney Laura Landenwich said, "Ms. Davis has the absolute right to believe whatever she wants about God, faith, and religion, but as a government official who swore an oath to uphold the law, she cannot pick and choose who she is going to serve, or which duties her office will perform based on her religious beliefs."