MOUNTAIN VIEW — In drought or drizzle, a group of abortion foes gathers on a sidewalk here each Thursday morning outside a Planned Parenthood clinic tucked in a nondescript strip mall next to a dry cleaner’s and a nail salon.

The hardy band of protesters remains well clear of the clinic, shooed away by Planned Parenthood volunteers wearing unmistakable blue-and-white vests. The landscaping between the sidewalk and parking lot serves as a de facto Mason-Dixon Line, separating the two sides in the irreconcilable conflict over abortion rights.

It is a line the U.S. Supreme Court is poised to re-examine, deciding by June how far government can go to keep protesters away from clinic workers and patients.

This scenario unfolds across the Bay Area each week, from a Planned Parenthood clinic in East San Jose where protesters gather on Mondays to the Friday morning prayer vigils outside another clinic in downtown Concord. Major cities such as Oakland, San Jose and San Francisco have limited how close protesters can get to clinics and the people who frequent them. Other communities, including Mountain View, rely on the fact the clinics are on private property and can police themselves.

It is not the first time the high court has dealt with the issue — but by revisiting the explosive question this term with a Massachusetts case, the justices are weighing a balancing act between the broad First Amendment right to protest and the worries of private patients and clinic workers who simply want to be left alone.

Bundled up recently outside the Mountain View clinic, Rita Donnelly, an elderly Peninsula woman who has protested at area clinics for decades, said she just wants to be able to get close enough to people to talk to them. Donnelly resembles Eleanor McCullen, the 77-year-old abortion foe who has led the Supreme Court challenge to the Massachusetts law that created a 35-foot buffer zone around clinics.

“Why wouldn’t they let people hear our side?” Donnelly asks, holding a sign supporting adoption alternatives.

But to abortion rights advocates and Planned Parenthood leadership, the answer to that question is simple: Violence and confrontation at many clinics over the years justifies the need to create buffer zones between patients and protesters and does not violate the First Amendment.

“We’re concerned about the ability of patients to enter (our clinics) without harassment or intimidation,” said Lupe Rodriguez, spokeswoman for Planned Parenthood Mar Monte, the Bay Area’s largest chapter. “We do have a constant presence of protesters, some more aggressive than others.”

Through the years, California has had a series of cases, including a major ruling from the state Supreme Court, permitting injunctions against protesters because of safety and privacy concerns. Seven California cities have local ordinances for the most part modeled after a 2000 U.S. Supreme Court ruling that upheld a Colorado law requiring protesters to stay at least 8 feet away from anyone who is within 100 feet of a clinic.

Beth Parker, statewide legal counsel for Planned Parenthood, worries that the Supreme Court may make it harder to maintain boundaries between protesters and patients if it invalidates the Massachusetts buffer zones. In fact, in oral arguments last month, the justices appeared concerned that Massachusetts went too far by interfering with protected free speech rights.

“I think it could reinvigorate the protesters,” Parker said. “And you might see more litigation.”

The Massachusetts 35-foot buffer zone, within which protesters are not allowed, is more restrictive than most laws, although San Francisco has a 25-foot buffer around entrances, exits and driveways to clinics that provide abortion services. San Francisco, joined by 17 other cities, filed arguments siding with Massachusetts in the case.

California, meanwhile, was among 13 states to back the Massachusetts law, arguing that states need the flexibility to secure “safe and unimpeded access to reproductive health care services.”

Legal experts say Massachusetts may be on shaky ground because it so strictly limited specific speech — abortion opposition — in a public setting. The question, they say, is whether the Supreme Court might scale back its 2000 decision upholding Colorado’s approach, which could hamper many local regulations across the country. Experts, however, predict the justices are more likely to opt for a more limited stance and conclude a 35-foot buffer zone is simply too expansive, leaving it up to cities and states to craft narrower laws.

“I think it’s going to be harder for states and cities to protect places like abortion clinics and (people coming and going from them) from speech that they’d probably like to avoid,” said Alan Brownstein, a UC Davis law professor.

Eugene Volokh, a UCLA law professor who argues the Massachusetts law violates free speech rights, said the buffer zones are meant in part to avoid “physical intrusion,” and “35 feet is way beyond that.”

That’s what worries protesters like 61-year-old David Zarri, who joins others from Contra Costa County Catholic churches on Fridays outside the downtown Concord Planned Parenthood clinic. Holding a rosary and a sign that reads, “Blessed Mother, Please Stop Planned Parenthood,” he argues that buffer zones infringe on his First Amendment right to free speech, assembly and religious expression.

“Where do you draw the line?” Zarri said. “Some say 35 feet. Some say 100. What’s to keep them from saying 1,000 feet?”

Zarri and other abortion foes, such as Phoebe Wise, a Los Altos woman who attends the Mountain View vigils, admit some protesters go too far. But they say they are unable to have even a quiet conversation with someone in the Planned Parenthood parking lot.

“We would like to be able to speak to people,” she said. “This way, right now, we have to shout. It’s not a good way to have a conversation.”

Bay Area News Group staff writer Lisa White contributed to this story. Howard Mintz covers legal affairs. Contact him at 408-286-0236 or follow him at Twitter.com/hmintz