By Dave Sebastian 



  Unions representing about 2,000 workers on a nine-month strike have offered to return to work at Asarco LLC, a Grupo Mexico subsidiary, ending a labor dispute, the United Steelworkers said Monday. 


  The strike's end comes after the National Labor Relations Board on June 15 alleged the mining, smelting and refining company of labor law violations that involve negotiations with unions, according to USW. The NLRB also said workers allegedly engaged in an unfair labor practice strike, the USW added. 


  Asarco and Grupo Mexico couldn't immediately be reached for comment. 


  The strike was in place at five copper mining and processing facilities in Arizona and Texas, the USW said. 


  "The best strategy for the most bargaining leverage is to end the current strike and make an unconditional offer to return to work," USW District 12 Director Gaylan Prescott said. 


  Write to Dave Sebastian at dave.sebastian@wsj.com