By Erwin Seba
HOUSTON (Reuters) - The largest U.S. refinery strike in 35 years entered its fourth week on Sunday as workers at 12 refineries accounting for one-fifth of national production capacity were walking picket lines.
Sources familiar with the negotiations said talks may resume by mid-week to end the walkout by 6,550 members of the United Steelworkers union (USW) at 15 plants, including the 12 refineries.
Representatives of both sides said no date has been set to restart negotiations, however.
The strike comes as U.S. workers seek more pay in a strengthening economy. Wal-Mart Stores Inc has said its U.S. workers will get a raise to at least $9 an hour, while West Coast port workers have reached a tentative deal for a new contract after a months-long dispute.
The refinery work stoppage began on Feb. 1 when talks for a new three-year contract between the USW and lead oil company negotiator Shell Oil Co broke down.
Talks were resumed but halted again after nearly reaching an agreement on Friday, said sources familiar with the negotiations.
After the latest breakdown between the two sides, Steelworkers leaders targeted Shell, which is the U.S. arm of Royal Dutch Shell Plc, calling workers out at a chemical plant and three refineries in the company's Motiva Enterprises [MOTIV.UL] joint-venture with Saudi Aramco [SDABO.UL].
The work stoppage now includes the nation's largest refinery, Motiva's 600,250 barrel per day (bpd) Port Arthur, Texas, refinery.
USW members are also picketing at Motiva's 235,000 bpd Convent, Louisiana, and 238,000 bpd Norco, Louisiana, refineries and the Shell chemical plant in Norco.
In a letter to striking employees at the Shell and Motiva plants, company officials said Shell has offered annual pay raises of 2 percent in each of the first two years of a proposed three-year pact and a 2.5-percent increase in the third year.
The company has also offered to study issues of worker fatigue, which has been cited as a factor in at least one fatal accident in the past 10 years.
Shell also told striking employees the key sticking point was non-union contractors who perform daily maintenance. The USW would like to see them replaced with union workers.
"Hiring flexibility is a proven way to protect our core Shell workforce and the long-term economic viability of our workforce," the letter said. "This strategy has served us all well, as we have not had to conduct any layoffs in decades."
A union spokeswoman declined comment on Sunday about the letter.
The Shell letter did not address the absence of "no-retrogression" language, which keeps agreements from previous contracts, including several on safety, in place. The lack of a no-retrogression clause has become a sticking point in talks, union leaders have said.