The group, Cowboys for Life, said they requested the school's permission to stage demonstrations at three well-trafficked areas on campus in October but were denied. Their lawyer, Brently Olsson, said the school's denial constituted a violation of the members' First Amendment rights, The Oklahoman of Oklahoma City said Tuesday.
Olsson said the protests were specifically shut down because of the graphic signs and leaflets used.
"The end result of abortion is very tragic," he said. "That side of the story, be it graphic, needs to be brought to people's attention."
The school's policy states officials may decline a group's facility usage request if it conflicts with another planned event, to avoid disruptions or maintain public order, the newspaper said.
A school spokesman declined comment, saying they hadn't yet seen the lawsuit.