Stitt signed bills last year that prohibit transgender girls and women from playing on female sports teams and prevent transgender children from using school bathrooms that correspond to their gender identity.

“Last year, I called for a statewide ban on all irreversible gender transition surgeries and hormone therapies on minors so I am thrilled to sign this into law today and protect our kids,” Stitt said in a statement released after the signing. “We cannot turn a blind eye to what’s happening across our nation, and as governor I am proud to stand up for what’s right and ban life-altering transition surgeries on children in the state of Oklahoma.”

The bill Stitt signed on Monday makes it illegal to provide gender-transition medical care for anyone under the age of 18. Such treatment can include surgery as well as hormones and drugs that suppress or delay normal puberty.

Transgender advocates and parents of transgender children say such care is essential.

Several civil liberty organizations, including the American Civil Liberties Union of Oklahoma, has promised to “take any necessary legal action” to prevent the law from taking effect.

“Gender-affirming care is a critical part of helping transgender adolescents succeed, establish healthy relationships with their friends and family, live authentically as themselves, and dream about their futures,” Lambda Legal, the ACLU and the ACLU said in a joint statement.

At least 16 states have now enacted laws restricting or banning gender-affirming care for minors.