By Teresa Carson

PORTLAND, Ore (Reuters) - A federal judge ordered a longshoremen's union on Friday to pay $250,000 in damages stemming from a long-simmering labor dispute at the Port of Longview in Washington state.

The local chapter of the International Longshore and Warehouse Union (ILWU) has been protesting for months against grain terminal operator EGT LLC's use of workers from a different union to staff its new Longview grain terminal.

The ILWU maintains that only workers it represents can be hired at Longview under a larger agreement it has with the overall port, located in southwest Washington near the Columbia River, about 40 miles north of Portland, Oregon.

While fewer than 50 jobs are at stake, the protests have escalated into clashes with police at times, and more than 200 arrests have been made since July.

Several longshoremen were arrested for blocking a train bound for the facility on September 7, and more than 500 port workers stormed the terminal the following day, damaging rail cars and other property.

U.S. District Judge Ronald Leighton in Tacoma, Washington, found the union in contempt of court for defying a restraining order he had issued against such actions, and ordered the ILWU Local 21 to pay $250,000 in damages.

He warned the union it faced fines for any future violations.

The union called the $250,000 damage assessment "rough justice" and said it planned to appeal. "We expect full vindication through the appellate process, including an overturning of today's unjust award," it said in a statement.

The money awarded by the judge is to be divided among EGT, local law enforcement, the Burlington Northern Santa Fe Railway Company and the National Labor Relations Board, which sought the court order against the union.

Protests have continued. A Thursday evening rally in a downtown Longview park drew hundreds of peaceful union supporters.

The union also has taken steps seeking to recall the sheriff of Cowlitz County, Washington, and has filed a civil rights suit against law enforcement, the city of Longview and the county for what it says is the "rough treatment" of longshore union members and supporters.

The protests on September 7 and 8 erupted despite a temporary restraining order the judge had issued days earlier. Leighton extended that order under a preliminary injunction on September 8.

"It is unfortunate that today's action was necessary. Our society is bound by the rule of law, and every individual and entity must be held accountable for their actions," EGT chief executive Larry Clarke said in a statement.

On Friday, Leighton was hearing arguments from the two sides over whether EGT's agreement with the port requires the company to hire ILWU longshoremen.

(Editing by Steve Gorman and Cynthia Johnston)