SACRAMENTO, Calif. (AP) — Thousands of scientists who work for California began a rolling three-day strike Wednesday — the first walkout by a state civil service union.

Members of the California Association of Professional Scientists marched under cloudy skies in Sacramento to protest lack of progress in contract talks. The walkout will spread to Los Angeles, Oakland and other cities on Thursday and Friday.

The union represents about 5,200 members who work in more than 50 state departments and deal with issues ranging from air pollution and toxic waste control to earthquake hazards and agricultural pests, according to its website.

Members have been without a contract since 2020 despite bargaining and mediation. The membership rejected a tentative agreement earlier this year. Another state mediation session is planned for Nov. 28.

It is the first time that state workers have struck since civil servants won collective bargaining rights in 1977, The Sacramento Bee reported.

“Nobody wants to be on strike, and nobody wants to be the first,” the union’s president, Jacqueline Tkac, told the Bee. “But it feels really inspiring to know that we have people that are so fired up about our situation that they’re willing to go out on strike for the first time and take that risk.”

Last week, the California Department of Human Resources filed a complaint of unfair labor practices against the union in an attempt to prevent the strike.

On Wednesday, the department said it was disappointed by the strike and that the state continues to bargain “in good faith.”

The state “will continue to work with CAPS to achieve a fair successor agreement as we have with other bargaining units,” department spokesperson Camille Travis said in an email.

The union’s main concern is higher wages. It says state scientists are paid 40% to 60% less than “comparable positions who have the same level of responsibility and do similar or identical work.”