HOUSTON (Reuters] – United Steelworkers union (USW), filed charges at the U.S. National Labor Relations Board. Chevron Corp (NYSE:) this week stemming from a strike at the company’s refinery in Richmond, California.

USW alleges Chevron has altered the terms and conditions of employment, refused information, committed coercive acts, and made coercive statement.

Deena McMullen, spokesperson for Chevron, stated that the company had not received the charges from the NLRB.

B.K. White, the first vice president for USW Local 12-5 which represents striking workers, stated that no progress was made with Chevron.

Last time the sides met at the bargaining tables was five weeks ago.

McMullen added, “We are making progress through frequent conversations and looking forward to all of our coworkers returning to work.”

The USW and Chevron have talked informally, but those “sidebar” meetings have not resulted in movement toward a resolution to the strike that began on March 21, White said.

Chevron fired a striking worker from its 245,271 barrels-per-day (bpd), refinery.

McMullen claimed that an employee was dismissed because he took actions which were unsafe, illegal or in violation of Chevron policy.

White claimed that the worker who was fired shouted at workers coming into the plant to replace him.

Chevron will continue to manage the refinery alongside temporary substitute workers, supervisors and managers.

White stated that 60 percent of the 500 strikers have since returned to the work at the refinery.

“We would expect a little higher number (to cross the picket line) because we’re an open shop,” he said.

A workplace with a union representing workers is called an open shop. Workers are not required to join the union.