The California Faculty Association and the CSU have been bargaining for a new contract since May and were unable to reach a deal ahead of Monday's strike date.
Even so, all 23 campuses would remain open, the CSU said, adding that individual faculty members would be responsible for canceling their classes.
"If students have not heard from their instructor that their class is canceled, they should assume that it is being held as scheduled and go to class," the CSU said in a statement.
The union posted images of its members walking picket lines on Monday but it was still too early to assess the impact of the walkout.
"In recent news reports, CSU management has only addressed our conflict over salary; they have completely ignored the issues of workload, health and safety concerns, and parental leave," union Vice President Chris Cox said in a statement.
The CSU is distinct from the University of California system, which had its own five-week strike by academic workers at the end of 2022.
The strikes have formed part of a resurgence for organized labor activism in California. Los Angeles Unified School District workers staged a three-day strike last year before settling on a contract, while Hollywood writers and actors also held lengthy walkouts.
Another potential strike was averted on Friday, when the Teamsters Local 2010 representing 1,100 skilled trade workers on 22 campuses reached a deal with the CSU.
The faculty union is seeking a 12% annual raise, which the CSU called "financially unrealistic."
The CSU said it has offered a 15% raise over three years, or 5% each year.
(Reporting by Daniel Trotta; Editing by Bill Berkrot)
By Daniel Trotta
