President Trump vowed to impose hefty fines on California after a transgender athlete won a high school track and field championship, stirring up national controversy.

Trump called out California Gov. Gavin Newsom (D-Calif.) over the situation, saying he knows the administration could enforce penalties for allowing the athlete to compete.

“A Biological Male competed in California Girls State Finals, WINNING BIG, despite the fact that they were warned by me not to do so. As Governor Gavin Newscum fully understands, large scale fines will be imposed!!!” Trump wrote on Truth Social.

The Justice Department threatened to take legal action against California public schools on Monday, arguing the state’s bylaw the allowed the transgender athlete to compete violated the Equal Protection Clause of the Constitution and discriminated against athletes on the basis of sex, The New York Times reported.

The athlete, AB Hernandez, competed after a rule change by the high school sports governing body and the athlete’s success in the championship has drawn national attention.

Trump signed an executive order in February that banned transgender athletes from competing in girls’ and womens’ sports after promising to do so on the campaign trail.

The order directs his administration to halt funding for schools that refuse the ban transgender athletes but some states have not compiled, including Maine.

Maine Gov. Janet Mills (D) has said the president’s order violates the state’s anti-discrimination law and Trump has argued the state is violating Title IX, which is the federal civil rights law against sex discrimination, by allowing trans girls to compete.