Story highlights The group says the professor erased their anti-abortion chalk messages

The students say they had school permission to write them

(CNN) A lawsuit filed by a student anti-abortion group against a California university professor claims he and some of his students infringed on their free speech rights when erasing chalk messages on campus.

According to the lawsuit, Fresno State Students for Life planned to write messages in chalk outside the university's library. After getting approval from the university, they set a date: May 2.

That morning, the group wrote their messages; examples ranged from "You CAN be pregnant & successful" and "Unborn lives matter" to "Women need love, NOT abortion."

Shortly before finishing, the lawsuit claims, William Thatcher, an assistant professor of public health, approached the group and said they had to keep their messages to the university's free speech area.

According to Bernadette Tasy, one of the organizers with the group and a plaintiff in the lawsuit, Thatcher then said he would be back to remove the messages. Tasy says he returned with a group of students and they attempted to remove the group's messages.

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