AMC Theatres has apologized to the Rev. William J. Barber II, a civil rights leader, after he was escorted from a Greenville, N.C., theater after employees refused to allow him to use a chair he needs to manage a painful medical condition, he said.

Mr. Barber, 60, was attending a Tuesday afternoon screening of “The Color Purple” with his mother, Eleanor Barber, 90. He said he tried to use the chair, which an assistant carried for him, by placing it in an area reserved for handicapped seating, saying he had done so before in theaters, at Broadway plays and even on a visit to the White House.

He said a theater employee told him that he would not be able to use the chair, which looks like a small stool, because it did not comply with guidelines in the Americans with Disabilities Act.

Employees then summoned the Greenville police and told the officers that they wanted Mr. Barber to leave or be charged with trespassing, according to Mr. Barber, who shared a video of the encounter with The New York Times.