* Talks continue with USW at 4 Tesoro refineries
* L.A., Washington, Utah workers vote to OK strike
* Hawaii, Utah Tesoro refinery workers OK pact
HOUSTON, April 5 (Reuters) - Workers at Tesoro Corp's 58,000 barrel per day (bpd) Mandan, North Dakota, refinery joined workers at two other of the company's refineries by giving local union leaders authority to call a strike, the United Steelworkers union (USW) said on Thursday.
The vote, taken on Wednesday night, does not mean workers at the Mandan or other refineries will walk off their jobs.
"If the company continues to refuse to put forward an offer that our membership can find acceptable, we will have to consider using our authority to call a strike," said Javier Montoya, president of the Mandan USW local.
A Tesoro spokeswoman said the independent western U.S. refiner would continue talks with the union.
"We continue to work toward ratification at each of our remaining USW-represented Tesoro locations," said Tesoro spokeswoman Tina Barbee.
Workers at Tesoro's 120,000 bpd Anacortes, Washington, and 166,000 bpd Martinez, California, refineries have already voted to authorize their local union leaders to call a work stoppage if negotiations fail.
USW members at Tesoro's 93,500 bpd Kapolei, Hawaii, and 57,500 bpd Salt Lake City refineries have voted to accept the company's contract proposals.
Negotiations are also continuing at Tesoro's 97,000 bpd Los Angeles Refinery in Wilmington, California.
USW officials have said Tesoro has made changes in the current contract without first negotiating with the union.
Also, the USW is seeking greater safety protections for workers at Tesoro's plants.
An April 2010 explosion at Tesoro's Anacortes refinery claimed the lives of seven workers. A Washington state investigation of the blast faulted Tesoro's maintenance of equipment at the refinery. Tesoro has challenged those findings.