Schenck v. Pro-Choice Network of Western New York, 519 US 357
The Supreme Court of the United States held a " floating buffer zone" (in which protestors could not approach within 15 feet of a person or vehicle entering or exiting abortion clinics) would unduly interfere with the First Amendment rights of the protestor.

Brief for Petitioners of the American Center for Law and Justice

Reply Brief for Petitioners

Oral Arguments - Official Transcript 95-1065

Opinion of the Court - Rehnquist. J.

Dissenting - Scalia, J.