Union chief says U.S. refinery strike could spread

(Adds unfair labor practice filed against union local)

HOUSTON, Feb 24 (Reuters) - The largest U.S. refinery strike in 35 years could spread if talks over improved safety conditions 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 provisions from previous contracts and tighten fatigue standards for workers, as well as win back daily maintenance jobs now done by non-union contractors.

"(The strike spreading) depends on what happens in the next round of negotiations and that those negotiations resume fairly quickly," Gerard in a telephone news conference from Atlanta (BSE: ATLANTA.BO - news) .

Gerard, who is attending the AFL-CIO winter conference in Atlanta, said no date has been set for resuming negotiations.

A Shell (LSE: RDSB.L - news) spokesman also said a resumption of talks had not been scheduled as of Tuesday morning. Shell Oil Co, the U.S. arm of Royal Dutch Shell Plc (Xetra: R6C1.DE - news) , is the lead oil company negotiator.

Talks broke off on Friday, after which the USW ordered workers at three Motiva refineries, including the nation's largest, which are co-owned by Shell, to walk off their jobs.

Sources familiar with the talks told Reuters on Monday that face-to-face negotiations may not resume this week.

Gerard also said a "handful" of USW members have crossed picket lines to return to their jobs at refineries and other plants.

The National Right To Work Legal Defense Foundation said on Tuesday that 150 workers out of 800 at the Shell Deer Park, Texas, refinery have continued working despite instructions to strike on Feb. 1.

The Foundation said it has filed an unfair labor practice charge with the U.S. National Labor Relations Board against the USW local union representing Deer Park workers for intimidation and 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 practice charges against most of the refineries where workers are on strike.

Gerard said fires or explosions have occurred every eight days on average since an April 2010 blast at Tesoro's refinery in Anacortes, Washington, which claimed the lives of seven workers.

"From 2010 to now, there have been 27 people who have been killed," Gerard said, referring to deaths from accidents at refineries. (Reporting by Erwin Seba; Editing by Chizu Nomiyama and Alan Crosby)