LOS ANGELES, CA — Thousands of University of California service workers began a three-day strike Monday at campuses and medical facilities across the state, including at UCLA and UC Irvine Medical Center.

Service workers represented by Local 3299 of the American Federation of State, County and Municipal Employees voted overwhelmingly last month to authorize a strike if no progress were made in negotiations. UC officials have repeatedly criticized the union for calling the strike, accusing the labor group of rejecting an offer of "fair, multi-year wage increases and excellent medical and retirement benefits."

The strike got off to a rocky start at UCLA, where a motorist apparently got impatient around 9:45 a.m., and tried to drive through the picketers crossing a street. Police and witnesses said a man in an SUV became irritated when union members were marching through the intersection of Westwood Plaza and Le Conte Avenue. Witnesses said the man initially got out of his SUV with some type of stick and threatened the picketers. "He jumped back into his car, he gasses it," one union member told KNX Newsradio. "I'm holding on to his hood. He brakes, I thought he was going to stop, and as soon as I'm trying to move he gasses it again and I just grabbed on again and as he's driving I'm telling him to slow down."

UCLA Police said three picketers were treated for minor injuries at the scene. The driver was taken into custody, although he appeared to have some difficulty breathing while being arrested and was taken to Ronald Reagan UCLA Medical Center to be checked out, police said. There were no other reports of any other clashes involving union protesters.

In light of the impasse in contract talks, the university system last month imposed contract terms on the union for the 2017-18 fiscal year, including 2 percent pay increases. The UC's latest contract offer to the union included annual 3 percent raises over the next four years, according to the university.

The union denounced the move to impose contract terms, responding by issuing a notice of a strike set to last until Wednesday.

"We've bargained in good faith for over a year to address the widening income, racial and gender disparities that front-line, low-wage workers at UC are living every day," AFSCME Local 3299 President Kathryn Lybarger said. "Instead of joining us in the effort to arrest these trends, UC has insisted on deepening them -- leaving workers no option but to strike." UC officials issued a statement saying they "strongly disagree with AFSCME's decision to strike, which will negatively impact patients, students and the UC community."