Unions representing about 2,000 hourly workers at five Asarco mining operations in Arizona and Texas voted overwhelmingly to strike against unfair labor practices, rejecting a final company offer in a vote on Friday.

Eight unions led by the United Steelworkers held meetings and strike-authorization votes this week after voting to authorize a strike earlier against Tucson-based Asarco, a subsidiary of Grupo Mexico.

Steelworkers District 12 Director Robert LaVenture said Asarco's four-year contract proposal "insulted union members at all of the facilities" by including no wage increase for nearly two-thirds of workers, freezing the existing pension plan, and more than doubling the out-of-pocket contribution individual workers already pay for health care.

After tallying votes late Friday, the Steelworkers provided a required 48 hours' notice to terminate the extension agreement under which the parties have worked since the last contract expired in December.

Picketing will begin simultaneously at Asarco's Arizona properties at 11 p.m. on Sunday and early Monday at its Amarillo, Texas, facility, the Steelworkers said in a news release.