Workers at Western Refining’s St. Paul Park refinery have voted overwhelmingly to authorize a strike that could shut down the plant as early as this weekend.

Members of Teamsters Local 120 voted 148-0 to authorize a strike, as contract negotiations have snagged over safety issues, union leaders said Wednesday.

Local 120 represents about 185 workers at the refinery, which is the main gasoline supplier to SuperAmerica stores.

The refinery is adding another unit to process oil into petroleum products, and the Teamsters believe that at least four positions should be added to operate it, said Chris Riley, a business agent for Teamsters Local 120.

The company has offered no new jobs to cover the new unit, Riley said, and the union claims workers are already stretched thin.

Gary Hanson, spokesman for El Paso-based Western, declined to comment on specifics.

“We continue to work to reach an agreement that is good for employees and good for the community,” he said.

The union and the company have been negotiating for the past month, union officials said. The refinery’s three-year contract expires at midnight Dec. 31.

A strike authorization vote means the union could opt to strike immediately after the contract expires, or at a later date — depending on the state of negotiations.

Last month, San Antonio-based Tesoro Corp. announced it would pay $4.1 billion for Western, which also has refineries in Texas and New Mexico. The deal, however, is not finalized.