Many non-profit institutions (the New York Museum of Natural History, and the Art Institute of Chicago, for example) list admission charges at their entrances, but also say that these prices are only a suggestion, and that you can actually pay less if you want to.
I was wondering whether this option to pay less than the suggested entry fee was only provided as a matter of courtesy, or whether it is some sort of legal requirement for such institutions? And if it is a legal requirement, what institutions fall into the category? And does this fall under state or federal law? Presumably the latter, as it would probably be related to their tax-free status.
I don’t think it’s a legal requirement. IIRC, it was Thomas Hoving, former director of the Metropolitan Museum of Art, who instituted the pay-what-you-wish system in order to increase attendance, and other museums have just followed his example. This has a bit of that story, though I don’t know how rigorous the research is. I’ll see if I can dig up a better source later.
I believe some tax-supported museums are required to be “free to all.” One of the ways to do this and still get some revenue is to ask for a “suggested donation.” Another is to have the main part of the museum free, but charge for “special exhibits.” A third is to charge admission, but have certain days with free admission.