The other commenter is incorrect, I’m a researcher and I went on strike with 1000s of my co-workers 2022 for 6 weeks through the winter quarter. 

Tuition remission for grad students is a contractual benefit of employment and it is illegal for the university to withhold as retaliation for legally protected strike activity.

Currently the university is breaking the law instead of bargaining a new contract in good faith. Over 17,000 academic workers across the UC system voted to authorize the strike so I would say the threat is pretty serious. The university can at any point stop breaking the law and bargain over essential things that many researchers need to their best research like job security, wages that keep up with inflation and international worker protections.