SACRAMENTO, Calif. — A state audit released Tuesday says the University of California system has not fully followed its own policies for hiring contract service workers.

Administrators haven’t ensured individual campuses are complying with policies to prevent hiring contract workers in place of UC employees, the audit said. Campuses must provide documentation to justify a decision to displace employees.

The audit, which reviewed 31 contracts by UC campuses, found low-wage contract workers on average receive $3.86 less per hour than comparable university employees. It also found campuses aren’t consistently using competitive bidding for contracts, potentially losing out on savings. It did not offer a total dollar amount of money that could’ve been saved.

It’s the latest critical audit of the UC president’s office. A different audit released in April said administrators hid tens of millions of dollars from the public, which the president’s office has disputed. That audit found the office needed to keep clearer budget plans and records.

The university system takes the contracting audit’s recommendations seriously and will improve its practices, UC President Janet Napolitano said.

“We welcome the constructive input, which aligns with the University’s proactive efforts to continually improve and strengthen its policies and procedures,” Napolitano wrote in a letter to the state auditor earlier this month in response to a draft of the audit.

The UC system has been undercutting the standards it negotiated with university employees by systematically hiring low-wage contractors, said Kathryn Lybarger, the president of the largest union of UC employees. She said the contracting audit highlighted problems she and her union have already pointed out to the university system.