A worker at Asarco's Silver Bell Mine sprays down pure copper plates, each weighing 100 pounds (on each side), at the mine.

David Sanders/Arizona Daily Star

Unions representing workers at Tucson-based copper producer Asarco LLC have filed charges of unfair labor practices against the company with the National Labor Relations Board, as they continue working without a contract.

The company in turn has filed NLRB charges against the unions, according to a member update posted on the website of the United Steelworkers, the lead union in the negotiations.

The union says it filed unfair labor practice charges “at most ASARCO locations,” alleging unspecified violations of the National Labor Relations Act.

Asarco has filed an NLRB complaint alleging the unions have been bargaining in bad faith, a charge the union labeled “completely unfounded and ridiculous.”

Neither Asarco officials nor union representatives could be immediately reached for further clarification or comment.

The NLRB investigates charges of unfair labor practices and may decide to issue a formal complaint, which may lead to hearings and possible sanctions.

The union said its bargaining committee last met with the company in early July and no new meetings have been scheduled, citing wage increases and retiree health care as major sticking points.

The nearly 2,000 union members who work in Asarco’s copper mines, smelters and refineries entered contract negotiations in June 2013. They are spread over five locations, including the Mission mine near Sahuarita, the Ray mine and smelter complex near Hayden and the Silver Bell Mine in Marana, and are represented by eight different unions.

The unions elected to terminate their contract with Asarco effective June 20, though workers remain on the job and the company says it will continue to honor the prior contract as negotiations continue.