FOX31's Kasia Kerridge details the Safeway and Albertson's union strike as more stores across Colorado join in.

Safeway employees at a Denver store walked out Monday, expanding a strike that started this weekend. The strike started small with workers at three stores in Estes Park, Fountain and Pueblo, and a Denver distribution center.

The union representing Safeway store employees in Colorado has given the required 72-hour notice that the strike is set to begin one minute before midnight on Sunday.

Currently, unfair labor practice strikes are limited to Safeway/Albertsons locations in just four cities: stores in Estes Park, Fountain and Pueblo, and a distribution center in Denver.

About 45,000 grocery workers have authorized a strike at Ralphs, Albertsons, Vons and Pavilions stores in Southern California to protest unfair labor practices.