Probably time, place, and manner regulations for expression in airports. https://www.lawa.org/news-releases/2002/news-release-5 https://www.lawa.org/news-relea

Probably time, place, and manner regulations for expression in airports. https://www.lawa.org/news-releases/2002/news-release-5 https://www.lawa.org/news-releases/2002/news-release-5 (very many U.S. airports now have free expression booths requiring a permit, and forbid some kinds of expressive conduct or solicitation elsewhere in the airport, which I think the courts are OK with)