"Frontline Service and Patient Care UC workers are on strike November 20 and November 21, to protest UC's bad-faith bargaining and unfair labour practices," said the American Federation of State, County and Municipal Employees (AFSCME) Local 3,299, a union representing over 35,000 service workers, patient care technical workers, skilled craft workers, and more at UC's 10 campuses, five medical centres, numerous clinics, research laboratories, and UC Hastings College of Law, Xinhua news agency reported.

"UC's illegal conduct - from showing up to negotiations without any authority to forge compromises to announcing that it will bypass bargaining altogether to impose higher healthcare costs on workers - has left workers who take care of students and patients every day with no choice but to go on strike," said the labour union in a statement.

"Our members are the people who, frankly, you don't see because the campuses are clean, the food's cooked, students are taken care of," said the union's executive director Liz Perlman in a Facebook post, adding "We do need to be taken care of, too."

About 4,000 members of another labour union at the university system, the University Professional and Technical Employees (UPTE)-CWA Local 9119, also joined the strike.

The UC officials said in a post on social media platform X that they hope labour unions "will work with us to reach a fair deal for these valued employees soon" and "will ensure operational continuity of essential functions, which includes patient care, continue at a level of excellence that UC patients, students, faculty and staff expect."

The UC officials said in a statement earlier this month they "fundamentally disagree with AFSCME's claims of bad faith bargaining and characterisation of unacceptable bargaining proposals."

"From January to May, the UC and AFSCME bargaining teams met 22 times and worked collaboratively on proposals for the UC AFSCME-represented employees," said UC officials, adding that the University's proposals include $700 million in economic increases for the labour union's members and a direct response to what the labour union had asked for the greater of a $25 an hour minimum wage or a 5-per cent across-the-board raise.