Workers at nine U.S. refineries are on strike because Shell walked away from the negotiating table, the president of the United Steelworkers Union said.

Workers at five refineries in Texas, two in California and one each in Washington and Kentucky left their stations after negotiations with Shell collapsed Sunday.

"Shell refused to provide us with a counter-offer and left the bargaining table," USW International President Leo Gerard. "We had no choice but to give notice of a work stoppage."

There was no statement from Shell, which is the lead company involved in labor negotiations with the union. The USW said the latest offer from Shell was the fifth to be rejected by the union, which represents 65 refineries in the United States and about 850,000 workers.

National labor negotiations are focused on better wages, benefits and working conditions at a time when some companies working in the exploration and production side of the energy sector are announcing staff reductions as profits slump.

Local unions are focused on site-specific conditions. Barry Klein, the general manager at the Deer Park, Texas, facility, shuttered by the strike, said he was surprised by the USW move at the national level.

His plant had reached a tentative labor agreement in July, but had enacted strike plans as a contingency.

"In the meantime, we remain committed to resolving our differences with the USW and hope to resume negotiations as early as possible to get our employees back to work," he said in a statement.

USW International Vice President Tom Conway the union was frustrated with overtime and dangerous working conditions, saying the oil companies "do not want to work with us" to improve the work environment.