The Justice Department on Wednesday opened an investigation into California's allowing trans girl athletes to compete in girls' sports.

The probe follows the California Interscholastic Federation, the governing board for state high school sports, announcing Wednesday that it opened track-and-field finals to more girls after allowing a male to compete.

On Tuesday morning, Trump threatened to withhold federal funds from California if the governor and fellow Democrats in the state continued to defy his executive order banning males from playing in women's sports.

The fight between Trump and California follows the state allowing AB Hernandez, a male athlete who identifies as a girl, to compete in the girls varsity triple jump, high jump, and long jump in the state finals after winning the Division 3 girls long jump and girls triple jump and placing seventh in the high jump at the Southern Section Division Finals on May 19, according to CIF results.

The DOJ sent legal notice letters to California Attorney General Rob Bonta (D), State Superintendent of Public Instruction Tony Thurmond (D), the Jurupa Unified School District, and CIF regarding its opening of an investigation to determine if a state law that permits males to participate on female sports teams at state schools is in violation of Title IX.

The probe will also determine whether the state, its senior legal, educational, and athletic organizations, and the school district are discriminating on the basis of sex.

“Title IX exists to protect women and girls in education. It is perverse to allow males to compete against girls, invade their private spaces, and take their trophies,” Assistant Attorney General for Civil Rights Harmeet Dhillon said in a statement on Wednesday. “This Division will aggressively defend women’s hard-fought rights to equal educational opportunities.”

The DOJ also announced that it filed a statement of interest in federal court, supporting a lawsuit filed by the group Save Girls' Sports on behalf of two high school girl athletes over whether the state law that the department is now investigating violates Title IX.

The lawsuit alleges that the California law “is harming hundreds – if not thousands – of female students by removing opportunities for female athletes to be champions in their own sports, robbing them of podium positions and awards, and creating unsafe and intimidating environments in their bathrooms and locker rooms.”