Texas has sued a Dallas doctor for allegedly providing gender-affirming care to transgender youths, marking a significant enforcement of recent Republican-driven bans.

Texas AG Ken Paxton has sued a doctor for providing gender-affirming care to young people in the state, in what’s believed to be the first such lawsuit in the nation.

The Republican attorney general said the lawsuit marked the beginning of his enforcement of Texas’ Senate Bill 14, which bans gender-affirming care for minors.

A law passed by the state Legislature last year prohibits doctors from performing “gender transition” surgeries on minors; it also forbids doctors from prescribing puberty blockers and cross-sex hormones to children.

The lawsuit claims pediatrician May Lau provided hormone treatments to at least 21 patients between the ages of 14 and 17.

The lawsuit from Texas Attorney General Ken Paxton marks the first enforcement action against a physician under Senate Bill 14.

Texas has sued a Dallas doctor over accusations of providing gender-affirming care to youths, marking one of the first times a state has sought to enforce recent bans driven by Republicans.