(Adds unfair labor practice filed against union local)
HOUSTON, Feb 24 (Reuters) - The largest U.S. refinery strikein 35 years could spread if talks over improved safetyconditions do not resume soon, United Steelworkers union (USW)International President Leo Gerard said on Tuesday.
A total of 6,550 USW members are on strike at 15 plants,including 12 refineries accounting for one-fifth of U.S.capacity. Union members work at more than 200 oil terminals,pipelines, refineries and chemical plants in the U.S.
The USW has said it is seeking to retain safety provisionsfrom previous contracts and tighten fatigue standards forworkers, as well as win back daily maintenance jobs now done bynon-union contractors.
"(The strike spreading) depends on what happens in the nextround of negotiations and that those negotiations resume fairlyquickly," Gerard in a telephone news conference from Atlanta.
Gerard, who is attending the AFL-CIO winter conference inAtlanta, said no date has been set for resuming negotiations.
A Shell spokesman also said a resumption of talks had notbeen scheduled as of Tuesday morning. Shell Oil Co, the U.S. armof Royal Dutch Shell Plc, is the lead oil companynegotiator.
Talks broke off on Friday, after which the USW orderedworkers at three Motiva refineries, including the nation'slargest, which are co-owned by Shell, to walk off their jobs.
Sources familiar with the talks told Reuters on Monday thatface-to-face negotiations may not resume this week.
Gerard also said a "handful" of USW members have crossedpicket lines to return to their jobs at refineries and otherplants.
The National Right To Work Legal Defense Foundation said onTuesday that 150 workers out of 800 at the Shell Deer Park,Texas, refinery have continued working despite instructions tostrike on Feb. 1.
The Foundation said it has filed an unfair labor practicecharge with the U.S. National Labor Relations Board against theUSW local union representing Deer Park workers for intimidationand coercion of those crossing the picket line.
The USW declined to discuss the statement by the Foundation.
As of Feb. 13, USW locals had files unfair labor practicecharges against most of the refineries where workers are onstrike.
Gerard said fires or explosions have occurred every eightdays on average since an April 2010 blast at Tesoro's refineryin Anacortes, Washington, which claimed the lives of sevenworkers.
"From 2010 to now, there have been 27 people who have beenkilled," Gerard said, referring to deaths from accidents atrefineries. (Reporting by Erwin Seba; Editing by Chizu Nomiyama and AlanCrosby)
