Republican President Donald Trump also has acted aggressively in other areas involving transgender people, including removing transgender troops from military service. In May, the Supreme Court allowed the ouster of transgender service members to proceed, reversing lower courts that had blocked it.

The Supreme Court will consider whether biological sex, not gender identity, determines who can be on a women's team.

The court is diving into the hot button issue of transgender athletes joining female sports teams. More than half the states have bans.