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Asarco, part of Mexico-based mining giant Grupo Mexico, had alleged in a federal lawsuit filed in January 2015 that an arbitrator exceeded his authority by ordering the company to pay a quarterly copper-price bonus to union workers who are not part of the company’s pension plan.

The unions say those unpaid bonuses now total more than $10 million.

Judge Stephen M. McNamee of the U.S. District Court in Phoenix ruled March 3 that an arbitrator acted properly in ordering the bonus payments to workers who are not part of the company’s pension plan.

But on March 31, Asarco filed a motion for reconsideration, which unions led by the United Steelworkers have opposed.

Asarco declined to comment on the case.

Manny Armenta, a Steelworkers subdistrict director, said in a prepared statement the unions will continue to fight for the copper bonuses and to negotiate for a fair contract with Asarco, which the union says acted illegally and in bad faith.

Hearings are under way at the National Labor Relations Board in Phoenix in a complaint the NLRB filed against Asarco. The agency alleges the company has refused to bargain collectively, bypassed union representatives and discriminated against employees exercising their union rights. Initial hearings in the case began in March and are pending in Phoenix.

Asarco’s labor agreement originally expired in June 2013 and was extended until the parties terminated it in June 2015.

In documents obtained from the NLRB under a Freedom of Information Act request, the company acknowledged that on Dec. 1, 2015, it unilaterally imposed terms of its “last, best and final� contract offer, after reaching a bargaining impasse “after more than two years of bargaining in good faith.�

The unions contend that a lawful impasse was not reached because of unfair tactics by Asarco.

In the federal court case, Asarco argues that the judge misapplied the law in upholding the arbitrator’s award. Arbitration awards are only appealable on very narrow grounds, including a finding that an arbitrator exceeded his or her powers.

Asarco has maintained that the arbitrator improperly rewrote the company’s labor agreement. The union contends both sides failed to recognize that the contract language in the contract would make new hires ineligible for the price bonus.

Beyond the bonuses, the union wants the judge to require Asarco to pay interest on the bonuses owed, which the company is also fighting.

The issue affects about 550 Asarco employees hired after June 30, 2011, and still employed as of March 2015, as well as 180 former hourly employees who were either terminated, on leaves of absence or were promoted to salaried employees, according to court documents filed by the unions and attributed to Asarco.

The documents show miners are owed individual amounts ranging from about $1,100 to more than $30,000, with the average owed about $13,000 according to a Star analysis of filed data.

Asarco operates the Mission Mine in Sahuarita south of ÃÛèÖÖ±²¥, the Silver Bell Mine in Marana, and the Ray Mine and Hayden smelter in Central ÃÛèÖÖ±²¥.