When Kaley Chiles welcomes therapy clients to her tranquil bungalow of an office, she offers loose-leaf tea and asks what brings them to counseling, what’s causing distress and how she can help them meet their goals.

Under a 2019 Colorado law, if clients under 18 tell her that their same-sex attractions are causing them stress, as a licensed therapist, she is forbidden from counseling them to change their sexual orientation. If they want to talk about their gender identity, she cannot advise them to change it.

Colorado lawmakers and major medical groups say that kind of counseling is ineffective and potentially harmful for minors, and it is therefore appropriate for state governments to outlaw it for licensed mental health professionals.

Mrs. Chiles, an evangelical Christian with a master’s degree in clinical mental health from Denver Seminary, says the law violates her First Amendment rights, constraining what she is allowed to say in therapy sessions with young people who have sought out her care.

“It seemed like an invasion for the state to kind of be peering into our private counseling sessions,” Mrs. Chiles said in an interview. “My speech is being censored because my clients are not able to see me and make certain goals that the state does not endorse.”

The Supreme Court will on Tuesday hear Mrs. Chiles’s challenge to the Colorado law, in a case with implications for more than 20 states with similar laws. It will now fall to the justices to decide whether Colorado’s law, as it applies to talk therapy, is about properly regulating medical treatment or impermissibly censoring speech.