(Adds Shell comment, USW declines further comment)
HOUSTON, Feb 19 (Reuters) - Union negotiators on Thursdayrejected the latest contract offer from oil companies and saidthe largest U.S. refinery strike since 1980 may spread to moreplants beyond the 11 where walkouts are underway.
The United Steelworkers union (USW) said in a message tomembers and news media including Reuters that the latestproposal from lead oil company negotiator Royal Dutch Shell Plc failed to improve safety at refineries and chemicalplants in an "enforceable way."
The union also told workers not on strike to be prepared towalk out in the coming days.
"New offer fails to improve safety in enforceable way," theUSW said in the text message. "All units instructed to rejectand prepare to join (unfair labor practices) strike if calledupon. Union at table ready to bargain."
A USW spokewoman confirmed the message, but said the unionwould have no further comment.
A Shell spokesman said the two sides had met on Thursday.
"We continue to be focused on reaching a mutuallysatisfactory agreement," said Shell spokesman Ray Fisher. "Weremain committed to maintaining safe operations as part of thenormal course of business. Out of respect for the bargainingprocess, we are unable to comment further on today'sactivities."
Earlier this week, the union's lead negotiator,International Vice President Gary Beevers, told Reuters thatsafe staffing levels at refineries and chemical plants were asticking point in the talks.
More than 5,000 workers at 11 plants, including ninerefineries accounting for 13 percent of U.S. productioncapacity, remained on strike on Thursday. They are seeking a newthree-year contract governing safety and pay.
The strike widened on Feb. 6 when workers at two refineriesoperated by BP Plc were told to walk off their jobs thefollowing day.
Only one refinery has shut down due to the strike.
Tesoro Corp's 166,000-bpd plant in Martinez,California, was scheduled for a partial shutdown for a plannedmulti-unit overhaul prior to the strike. Company officialsdecided to idle the entire plant after the walkout began.
Tesoro officials have said production will not resume forthe duration of the strike.
The USW is seeking a three-year, industrywide pact thatwould cover 30,000 workers at 63 U.S. refineries that togetheraccount for two-thirds of domestic capacity.
Companies have called on temporary replacement workers tokeep plants running at nearly normal levels. (Reporting by Erwin Seba; Editing by Toni Reinhold)
