Asarco operates the Mission Mine in Sahuarita, among others.

Copper miners on both sides of the border are accusing parent company Grupo Mexico and its U.S. subsidiary, Asarco, of violating workers’ rights.

A complaint was filed Thursday with the U.S. National Contact Point for the Organization for Economic Cooperation and Development Guidelines on Multinational Enterprises, asking for mediation.

The specific contents of the complaint are confidential, but the United Steel Workers and the National Union of Mine, Metal, Steel and Allied Workers of the Mexican Republic accuse Tucson-based Asarco of multiple unfair labor practices in the United States, including threatening workers, unlawfully implementing changes in workplace conditions, and failing to negotiate with the unions at the company’s five U.S. facilities.

More than 2,000 workers have been working at Asarco’s copper mines and processing facilities under the terms and conditions of a labor agreement that expired in June 2013 but was extended until the parties terminated it in June 2015.

β€œAsarco has used intimidation, manipulation and discrimination to interfere with workers attempting to exercise their rights,” USW International President Leo W. Gerard said in a statement. β€œCompanies like Grupo Mexico, and other multinational conglomerates that attempt to silence workers, are precisely the reason why international solidarity among labor unions is so important.”

Asarco officials did not respond to a request for comment Friday.

The filing by the two unions comes as workers prepare to mark the 10th anniversary of an explosion at the Grupo Mexico mine at Pasta de Conchos in the state of Coahuila that killed 65 workers. The bodies of 63 miners remain trapped underground. Representatives of the USW will join Los Mineros members for a march this weekend in Mexico City to demand recovery of the bodies, compensation for the families of the victims, and prosecution of the responsible company and government officials.

It is the latest allegation against the copper company in its years-long clash with workers.

Last month, the National Labor Relations Board issued an amended complaint against Asarco alleging the company unlawfully implemented its β€œlast, best and final offer” though bargaining had not reached a good-faith impasse.

The NLRB charged that the company had refused to bargain collectively with the United Steelworkers and seven other unions, which have represented Asarco employees since 2007.

Asarco was ordered to file a written response and a hearing on both complaints has been set for March 15 in Phoenix. Company officials have not publicly commented on the dispute.

Asarco operates the Mission Mine in Sahuarita south of Tucson, the Silver Bell Mine in Marana and the Ray Mine in central Arizona and a smelter in Hayden.


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