Kaiser Permanente mental health workers picketed outside the Woodland Hills Medical Center on Thursday as part of a weeklong strike for increased staffing and resources at Kaiser hospitals across the state.

The strike is organized by the National Union of Healthcare Workers, which claims that Kaiser medical centers lack the necessary staff to provide patients with safe and timely mental health services. The group says 4,000 psychologists, therapists, social workers, psychiatric nurses and addiction medicine specialists are participating in the walkout.

“Kaiser clearly has the resources to be a mental health care leader; instead it’s a violator of mental health access rules,” said NUHW President Sal Rosselli in a statement. “We remain ready to work with Kaiser to fix its mental health system, but it’s time for Kaiser to use its vast resources to make meaningful improvements for patients.”

In a statement, Oakland-based Kaiser Permanente said the union is striking to gain leverage in ongoing contract negotiations.

“For the past three years, while we had a contract in place with NUHW, it did not engage in this kind of behavior,” Kaiser said in a statement. “Now that we are in negotiations with the union to renew our contract, which expired on Sept. 30, union leadership is using negative tactics to pressure Kaiser Permanente during bargaining.”

Today was the fourth day of the statewide strike and the first day that employees picketed in Woodland Hills. It is unclear whether the protest will continue but no other strike dates are currently planned at the local center, according to the NUHW’s website.

Kaiser employees have walked out at hospitals in cities including Los Angeles, San Diego, Anaheim, Sacramento and San Francisco. The health provider said medical centers will remain open during the strike but that some non-urgent mental health visits may need to be rescheduled.