No pants

My daughter was amused by the unintended ambiguity of this sentence:

Few restaurants enforce a coat-and-tie dress code for men or a no-pants policy for women.

Connie Eble, "Slang." Language in the U.S.A.: Themes for the Twenty-first Century, ed. Edward Finegan and John R. Rickford (Cambridge University Press, 2004)

Just what would a no-pants policy prohibit?

(Thanks, Rachel!)