Clark v. Community for Creative Non-Violence, 468 US 288 - Supreme Court 1984
The issue in this case is whether a National Park Service regulation prohibiting camping in certain parks violates the First Amendment when applied to prohibit demonstrators from sleeping in Lafayette Park and the Mall in connection with a demonstration intended to call attention to the plight of the homeless. We hold that it does not and reverse the contrary judgment of the Court of Appeals.
Supreme Court case backs that up.
Also from the case "Expression, whether oral or written or symbolized by conduct, is subject to reasonable time, place, or manner restrictions. We have often noted that restrictions of this kind are valid provided that they are justified without reference to the content of the regulated speech, that they are narrowly tailored to serve a significant governmental interest, and that they leave open ample alternative channels for communication of the information."