Updated

A Pacific Northwest grain terminal owner imposed a lockout on longshoremen Wednesday after saying an "independent former FBI investigator" determined a union leader sabotaged company equipment at the height of contentious labor problems in December.

United Grain Corp., part of the Japanese conglomerate Mitsui & Co., said nonunion replacement workers will operate its Vancouver, Wash., export terminal for an "indefinite" period. The company said it fired the union leader, whom it described as a member of the bargaining team of Local 4 of the International Longshore and Warehouse Union but did not name.

"Deliberate attempts by an ILWU leader to damage equipment, disrupt operations and put co-workers at risk cannot be tolerated," United Grain CEO Gary Schuld said Wednesday.

The union called the company's allegations unfounded, and locked-out longshoremen immediately picketed outside the terminal.

"United Grain and its Japanese owners at Mitsui have failed to negotiate in good faith with the men and women of the ILWU for months, and instead chose to aggressively prepare for a lockout, spending enormous resources on an out-of-state security firm," ILWU spokeswoman Jennifer Sargent said in a statement. "Mitsui-United Grain has fabricated a story as an excuse to do what they've wanted to do all along, which is to lock workers out instead of reach a fair agreement with them."

Late last year, the company was among Northwest terminal owners who declared an impasse on labor negotiations and imposed a contract that included new, management-friendly workplace rules.

Columbia Grain said the sabotage occurred Dec. 22, days before the impasse was declared. In one case, someone shoved a 2-foot-long metal pipe into a conveyor, causing it to shut down, the company said. In another, a vandal damaged a gear box with a mixture of sand and water.

The company, in a letter sent to the union, said an "impartial and independent" former FBI investigator determined the union leader was the culprit following an investigation that included interviews, surveillance tapes and other evidence.

No charges have been filed, but Schuld said the investigator's report will be turned over to law enforcement

More than a quarter of all U.S. grain exports move through nine grain terminals on the Willamette River and Puget Sound. The contract dispute initially involved six of those terminals that operate under a single collective bargaining agreement with the ILWU: United Grain, based in Vancouver; Columbia Grain, based in Portland; Louis Dreyfus Commodities, which has grain elevators in Portland and Seattle; and Temco, which has elevators in Portland and Tacoma, Wash.

United Grain has the largest storage capacity of any West Coast grain export facility with more than 7 million bushels of storage, according to the company's website.

The U.S.-owned Temco broke away from the alliance in early December and negotiated separately with the union. They announced a five-year agreement Wednesday.

"It's no coincidence that Mitsui-United Grain has chosen to throw out unfounded charges by an unnamed 'investigator' just days after the union membership ratified an agreement with Mistui-United Grain's American competitors," Sargent said.

The pro-management terms implemented in December eliminate some employee perks and grievance procedures while giving employers more discretion in hiring and staffing decisions. Management, for example, can expand shifts to 12 hours, if needed, and use elevator employees to help load ships.