The Supreme Court unanimously struck down the 35-foot protest-free zone outside abortion clinics in Massachusetts Thursday, declaring it an unconstitutional restraint on the free-speech rights of protesters.

Authorities have less intrusive ways to deal with potential confrontations or other problems that can arise outside clinics, Chief Justice John Roberts wrote. Roberts noted that most of the problems reported by police and the clinics in Massachusetts occurred outside a single Planned Parenthood facility in Boston, and only on Saturdays when the largest crowds typically gather.
   
‘‘For a problem shown to arise only once a week in one city at one clinic, creating 35-foot buffer zones at every clinic across the Commonwealth is hardly a narrowly tailored solution,’’ Roberts said. He wrote the majority opinion after asking no questions — exceedingly rare for him — at the argument in January.

Roberts noted that no other state has a similar law and that he is aware of only five cities that have created fixed buffer zones around abortion clinics: Burlington, Vermont; Pittsburgh; Portland, Maine, and San Francisco and Santa Barbara in California.

The ruling also left intact a high court decision from 2000 that upheld a floating buffer zone in Colorado.