A law that keeps protestors away from Massachusetts abortion clinics is being challenged in the U.S. Supreme Court.

The case pits abortion rights against free speech. The Massachusetts law bars protests within 35 feet of abortion clinics.

"This law creates an area of safety around the entrances so that our patients and staff can gain access to our health centers safely and without people blockading the doorways," said Planned Parenthood Massachusetts CEO Marty Waltz, a former state representative who sponsored the so-called "buffer-zone law" in the legislature.

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Critics of the law say it's an infringement of their First Amendment rights. In a Supreme Court brief, activists say they want to peacefully hand out literature and talk to women who are considering abortion. They say the buffer zone makes that impossible.

In 2000, the Supreme Court upheld a different buffer zone law in Colorado. But the court has become more conservative since then. Arguments in the case begin on Wednesday.