Unionized instructors across the 23-campus California State University system began taking a strike vote today, casting ballots on whether to stage “rolling walkouts” that would send professors to picket lines for two days at a time, from one campus to the next.

The California Faculty Association, the union holding the vote, represents about 24,000 professors and instructors in the system. If the union calls a strike, it could be the largest job action by professors in the history of American higher education.

The union’s contract negotiations with the university system have stalled, and the contract is being reviewed by a third-party fact finder, who will issue a report this month. The union is not satisfied with the contract’s salary provisions.

This week, from today through Thursday, union members on 16 of the system’s campuses will vote on whether to authorize the union’s Board of Directors to call the strike. Professors on the remaining seven campuses will cast their ballots from March 12 to 15. John Travis, the union’s president and a professor of political science at Humboldt State University, said he thought the strike authorization would win approval. “We hope and expect it to be positive,” he said.

The union will announce the results of the vote on March 21.