SANTA CRUZ — More than 12,000 fall-quarter grades — about 20% of the total — remained outstanding as of Sunday as the UC Santa Cruz grading strike continued into the new year.

Demanding a raise they say would allow them to afford the high cost of living in Santa Cruz, scores of UCSC teaching assistants and graduate-student instructors refused to submit students’ fall quarter grades by a Dec. 18 deadline.

Some striking students claim they spend upward of 70% of their wages — typically, about $2,400 a month for nine months of the year — to afford housing in one of the nation’s least affordable rental markets. They are demanding a $1,412 cost-of-living adjustment they argue would provide wage parity with graduate student workers at UC Riverside.

Complicating any potential resolution, the strike is not authorized by the UAW 2865 union that represents graduate-student workers across the University of California. The contract setting the graduate students’ wages was negotiated between the union and the UC at the system level, and UCSC officials insist they are unable to negotiate directly with the students.

In a campus message Monday, the first day of the winter quarter, interim provost Lori Kletzer announced that 80% of fall quarter grades had been submitted.

“Grades belong to the students who earned them, and we will continue to work toward full grade submission,” Kletzer said in the message.

The 80% figure is based on the 63,414 individual grades expected based on fall quarter enrollment across all undergraduate and graduate courses, according to campus spokesman Scott Hernandez-Jason.

As of Sunday, 12,312 of those individual grades remained outstanding.

The figure suggests a large number of graduate students followed through with threats to withhold grades — though exactly how many, and across which departments, remained unclear.

Hernandez-Jason said Wednesday he was unable to release any additional information that would shed further light on the extent of the strike. “That’s all I have at the moment,” he said.

Graduate student organizers characterized the strike as “remarkably widespread” in a Monday news release.

“While no authoritative survey of student participation has been possible to conduct thus far, information we have received indicates that more than half of graduate students participated by refusing to submit grades,” the release states.

The students said they planned to discuss the ongoing action collectively at a strike meeting scheduled for Jan. 9.

In Monday’s campus message, Kletzer, the interim campus provost, said UCSC is “actively working” on solutions to students’ housing needs.

“However, unauthorized labor actions (such as withholding grades) slow processes and close communication paths,” Kletzer said in the message. “This unauthorized action has made meeting and working together impossible … and has delayed the implementation of plans to better support graduate students.”

“While we recognize the importance of free speech and the exchange of ideas, students involved in the unsanctioned work stoppage have engaged in potential misconduct and may be subject to disciplinary action,” the message continued.

UCSC Chancellor Cynthia Larive has yet to publicly address the strike.

Dozens of UCSC carpenters, plumbers and electricians began a separate strike Monday over stalled contract negotiations.