Ten US states have sued the federal government over rules requiring schools to allow transgender students to use toilets conforming to their gender identity.
The lawsuit was filed in federal court in Nebraska and included nine other states: Arkansas, Kansas, Michigan, Montana, North Dakota, Ohio, South Carolina, South Dakota, and Wyoming.
The filing comes after 11 states sued in May over the same government directive. North Carolina officials also sued the federal government in May over the same issue.
Vast sums of federal funding are at stake. The money could be withheld from public schools that refuse to comply with the federal directive.
Nebraska attorney general Doug Peterson said the US Education Department and Justice Department have circumvented established law and the process for changing existing laws.
"It also supersedes local school districts' authority to address student issues on an individualised, professional and private basis," the release said.
The battle began to take shape when officials in Charlotte passed a sweeping anti-discrimination ordinance that included a provision allowing transgender people to use toilets that correspond to their gender identity. North Carolina passed a law nullifying that ordinance and banning others like it.
Soon after, the Justice Department said the law violated the federal Civil Rights Act and said it could not be enforced. US attorney general Loretta Lynch has said North Carolina's law requiring transgender people to use public toilets and showers corresponding to the gender on their birth certificate amounts to "state-sponsored discrimination" and is aimed at "a problem that doesn't exist".
The Nebraska lawsuit hinges on the terms "sex" and "gender identity", saying federal law uses only the term "sex".
"Neither the text nor the legislative history of Title IX supports an interpretation of the term "sex" as meaning anything other than one's sex as determined by anatomy and genetics," the lawsuit says.