HOUSTON (Reuters) - Independent western U.S. refiner Tesoro Corp and United Steelworkers union (USW) Local 5 continued talks on Friday aimed at preventing a strike at the company's largest refinery, a Tesoro spokeswoman said.

Meeting with a federal mediator for a third day, Tesoro and the USW hope to resolve disputes about worker safety and benefits that could otherwise lead to a strike at Tesoro's 166,000 barrel per day (bpd) San Francisco Bay-area refinery in Martinez, California.

USW members at the Tesoro refinery have already authorized local union leaders to order a strike if the talks failed to yield an agreement.

(Reporting by Erwin Seba; Editing by Gerald E. McCormick)