The United Steelworkers union has issued a strike notice in south Louisiana to two refineries and a chemical plant, with union workers set to go out at midnight Saturday.

Several hundred workers at Motiva refineries in Convent and Norco and at a Shell Chemical plant in Norco will join workers striking at other refineries around the U.S. if a contract agreement is not reached with the union by then, USW officials said.

A work stoppage was launched at midnight Friday at the Motiva Enterprises refinery in Port Arthur, Texas. Motiva said its three refineries will continue operating under prearranged contingency plans.

Some 1,350 union workers are employed at the three Louisiana facilities and the Port Arthur refinery.

Eleven refinery facilities across the U.S. employing 5,200 workers are already on strike over what the union said are inadequate staffing levels, worker fatigue and safety issues.

Those 11 refineries — and the Port Arthur facility that went on strike at midnight Friday — account for 18.5 percent of U.S. production capacity.

“The industry’s refusal to meaningfully address safety issues through good faith bargaining gave us no other option but to expand our work stoppage,” said USW International President Leo W. Gerard.

On its website, Shell company officials decried the strike tactics.

“We believe this move sets the wrong tone for both parties to move forward and reach an agreement,” the website states. “We remain committed to continued safe operations and productive negotiations.”

Motiva said it has activated contingency plans to ensure a safe and orderly handover of operations from union workers at its two Louisiana facilities and the one in Port Arthur to “fully trained and qualified Motiva employees, who will safely operate the refineries.”

Motiva said contingency plans are updated 12 months in advance of labor contract negotiations to ensure operations continue.

The USW strike began Feb. 6 at nine refineries in Texas, California, Kentucky and Washington after talks broke down between Royal Dutch Shell and United Steelworkers. The strike has spread as contracts expired at other facilities.

Shell is the lead company in national contract negotiations with the USW, setting the stage for the union’s talks with other companies. The union represents workers at about 65 U.S. refineries.

The two Louisiana Motiva refineries are jointly operated by Royal Dutch Shell and Saudi Refining Inc., of Saudi Arabia. The chemical plant in Norco is operated by Shell.

The steelworkers say the sticking point doesn’t involve wages but rather staffing levels and overworked employees, health and safety issues and health care.

“Our members are speaking loud and clear,” said Gary Beevers, USW International vice president who oversees the union’s oil sector. “If it takes a global fight to win safe workplaces, so be it.”

Lynne Hancock, a spokeswoman for the union, said previously that while refiners appear fully staffed on paper, workers are routinely pulled out on temporary assignments.

Those assignments may last years, she said. Remaining workers have to work lots of overtime to pick up the slack, and eventually, those extra hours lead to tired employees. Tired workers are more likely to make mistakes, and those mistakes could lead to catastrophe, she said.

Included in the current round of negotiations is the ExxonMobil refinery in Chalmette, but no strike action has been taken there.

Overall, 3,100 Louisiana refinery workers are covered by the same contract.

Officials have said none of ExxonMobil’s Baton Rouge sites are involved in the National Oil Bargaining negotiations. Those facilities will be in the next round of negotiations. However, ExxonMobil’s Baton Rouge representatives and local union leaders have been meeting and working to resolve local issues.

Chevron’s chemical additives unit in Belle Chasse also is in the next round.

The USW represents 850,000 workers in North America employed in industries that include metals, rubber, chemicals, paper, oil refining, plus the service and public sectors.