SAN FRANCISCO (CBS SF) — Hundreds of workers are staging a strike against oil refineries in California and the Western U.S.

One of those about to be affected is the Tesoro plant in Martinez, which employs more than 400 people.

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The United Steelworkers Union called for its refinery workers to stage their largest walkout in more 30 years Sunday, saying its negotiations with Shell Oil Co. broke down less than two weeks after they began.

The union asked about 3,800 workers at nine refineries mostly in Texas and California to strike shortly after their previous contract expired after midnight.

Negotiations over a new contract started Jan. 21. The call for a strike happened after United Steelworkers, or USW, rejected Shell’s fourth contract offer. The union said Shell refused to provide a counter offer and that the company’s representatives had left the bargaining table.

The Tesoro plant in Martinez has more than 400 workers. They plan to join the strike as soon as the refinery can be shut down safely, likely to happen on Monday.

UC Berkeley professor and economic analyst Severin Borenstein says gas prices will not go up immediately, but if the strike drags on, consumers can expect to pay more.

“Some of the refineries probably won’t be able to keep up with their usual production, and California runs on a very tight supply and demand balance,” Borenstein.

USW Spokeswoman Lynne Hancock said the union wants a three-year contract and is focused on health care costs, safety, the use of contractors and staffing concerns, as well as wages.

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United Steelworkers represents about 30,000 workers at refineries, terminals, petrochemical plants and pipelines across the country. Shell is serving as the lead company in national oil bargaining talks with the union.

Any agreement reached between the union and Shell would then be used as a pattern for negotiations involving local unions.

The union called for a strike at the Marathon Galveston Bay Refinery in Texas City, Texas, the Shell Deer Park Refinery in Deer Park, Texas, and the Tesoro Carson Refinery in Carson, California, among other locations.

Shell said its Deer Park operation has started strike contingency plans and will continue operations “in the normal course of business.” It did not elaborate on the plans in a brief statement.

The remaining sites not targeted for a strike will operate under contract extensions that renew every 24 hours until one side in the negotiations decides that they have reached an impasse, Hancock said.

She added that negotiators normally reach an agreement on a new deal by the time these national contracts expire, or they extend the contract a few days to continue negotiations.

“We haven’t had a work stoppage like this since 1980,” she said.

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