BOSTON — A couple of mornings a week, Eleanor McCullen stakes out a spot outside the Planned Parenthood clinic here and tries to persuade women on their way in to think twice before having an abortion.

But she has to watch her step. If she crosses a painted yellow semicircle outside the clinic’s entrance, she commits a crime under a 2007 Massachusetts law.

Early last Wednesday, bundled up against the 7-degree cold, Ms. McCullen said she found the line to be intimidating, frustrating and a violation of her First Amendment rights. The Supreme Court will hear arguments on Wednesday in her challenge to the law.

The state’s attorney general, Martha Coakley, who is the lead defendant in the suit, said the 35-foot buffer zone created by the 2007 law was a necessary response to an ugly history of harassment and violence at abortion clinics in Massachusetts, including a shooting rampage at two facilities in 1994.