The justices ruled that Tennessee’s law, which prohibited some medical treatments for transgender youths, did not violate equal protection principles.

The court’s decision allows the law in Tennessee and has implications for the 23 other states that have banned similar treatments in recent years.

The conservative Supreme Court dealt a significant blow to transgender Americans on Wednesday, issuing a sweeping decision that may have implications beyond the medical care that was at center of one of the court’s highest-profile disputes this year.