WASHINGTON — With just days left to submit public comments on a National Park Service proposal to alter how protests are handled in the District of Columbia, civil rights advocates have issued urgent calls to oppose the measures, saying they would violate First Amendment rights.

The proposal, which was introduced in August, floats more than a dozen changes to how the Park Service facilitates protests, including how many demonstrators may gather on national parks’ land without a permit, what areas protesters can demonstrate in, and whether protesters should be required to reimburse the agency for the support and security it provides.

Constitutional experts immediately cast doubt on whether imposing fees on groups exercising their First Amendment rights would pass constitutional muster, and protest organizers said having to pay fees would discourage people from demonstrating.

Lawyers with the American Civil Liberties Union are scrutinizing other parts of the proposal, including limits on where protesters can stand on the sidewalk outside the White House.

The organization issued a public response to the Park Service that includes a point-by-point takedown of the proposals.

“The heart of the matter is clear: President Trump might not like having protesters on his doorstep, but the First Amendment guarantees their right to be there,” Arthur Spitzer, legal co-director of the American Civil Liberties Union of D.C., wrote in a blog post Tuesday explaining the organization’s opposition.

“Fee requirements could make mass protests like Martin Luther King Jr.’s historic 1963 March on Washington and its ‘I have a dream’ speech too expensive to happen,” Spitzer wrote in the blog post.