Safeway workers in several Colorado cities entered the third day of labor strikes Tuesday against Safeway and Albertsons over alleged unfair labor practices, with picketing in Grand Junction prompting a temporary store closure.

Workers at Albertsons, Pavilions, Ralphs and Vons grocery stores will begin preparations on Thursday for a possible strike.

Union members of the United Food and Commercial Workers (UFCW) in Southern California and the Pacific Northwest have voted this week to authorize a worker strike against Kroger and Albertsons stores, Supermarket News reported.

On Sunday, four stores went on strike including stores in Estes Park, Pueblo and Fountain, as well as a distribution center in Denver.

With the clock winding down toward Saturday night's deadline for new contract negotiations, a Colorado union has announced locations where grocery employees are set to walk off the job on Sunday in protest.

The union will take strike authorization votes this week after filing unfair labor practice charges against the companies last week.