A fight between the Obama administration and North Carolina over a state law limiting public bathroom access for transgender people has escalated as both sides sue each other, trading accusations of civil rights violations and government overreach.
The US Justice Department's complaint on Monday asked a federal district court in North Carolina to declare that the state is violating the 1964 Civil Rights Act and order it to stop enforcing the ban.
Hours earlier, North Carolina's Republican governor Pat McCrory and the state's secretary of public safety sued the agency in a different federal court in North Carolina, accusing it of "baseless and blatant overreach".
The so-called bathroom law, passed in March and known as HB 2, prohibits people from using public restrooms not corresponding to their biological sex.
It has thrust North Carolina into the centre of a national debate over equality and privacy.
By passing the law, North Carolina became the first state in the country to ban people from using multiple occupancy restrooms or changing rooms in public buildings and schools that do not match the sex on their birth certificate.
US Attorney General Loretta Lynch said on Monday the department "retains the option" of curtailing federal funding to North Carolina unless it backs down.
"None of us can stand by when a state enters the business of legislating identity and insists that a person pretend to be something or someone that they are not," Lynch said at a news conference, comparing the measure to Jim Crow-era racial discrimination laws and bans on same-sex marriage.
Lynch said the department is monitoring other US jurisdictions that have passed or considered laws similar to North Carolina's.
North Carolina Republicans say the law stops men from posing as transgender to gain access to women's restrooms.
McCrory told reporters that North Carolina had been forced to pass the law after the Charlotte city council passed an ordinance that allowed transgender people access to bathrooms based on gender identity in public and private buildings.
"We're taking the Obama admin to court. They're bypassing Congress, attempting to rewrite law & policies for the whole country, not just NC," McCrory wrote on Twitter.
The Republican leaders of North Carolina's state legislature also sued the US government over the law on Monday, hours after McCrory's lawsuit.
The law is also being challenged in federal district court by critics including the American Civil Liberties Union.