Grocery workers at several Safeway stores around Colorado began their strike Sunday and more are set to join.

The strike began at stores in Estes Park, Fountain, Pueblo, and a distribution center in Denver. On Monday, two more stores in Littleton and Castle Rock joined the picket lines.

It’s a stark contrast to when the union went on strike against King Soopers earlier in the year, when thousands of workers in the Denver metro area walked out of work at once.

United Food and Commercial Workers Local 7, the chapter representing unionized grocery workers in Wyoming and Colorado, has been negotiating with Safeway and its parent company Albertsons for more than nine months over new contracts.

Are Colorado’s King Soopers and Safeway stores both at risk of a strike?

After failing to reach a resolution over issues such as addressing overstaffing and employee benefits, a majority of workers in parts of the state including the Denver metro area voted to authorize a strike.

Monday’s protests grew by two stores to include the location on Broadway and Mineral Avenue in Littleton and 880 S. Perry St. in Castle Rock.

“Even if you are not on strike tomorrow, your store may be pulled within the next coming days,” UFCW Local 7 President Kim Cordova said in a YouTube message posted Saturday.

Union workers in Colorado Springs and Northern Colorado (including Fort Collins, Greeley, Loveland and Longmont) are voting Monday and Tuesday on whether or not to authorize joining the picket lines.

A Safeway spokesperson said in a statement Sunday that the grocery chain is committed to continuing productive conversations with the union and stores will remain open.

“We respect the rights of workers to engage in collective bargaining and are negotiating in good faith to achieve an agreement,” the spokesperson said. “Our focus remains on providing exceptional service to our customers and fostering a positive working environment for our associates.”

The union has also been in discussions with King Soopers, the Colorado chain operated by Kroger, over worker contracts for months.

The organization believes Safeway and King Soopers, who are direct competitors to each other, are “holding hands” in rolling back on contract negotiations.

Union leaders said hitting one grocer is also a message to the other grocery chain.

King Soopers workers stopped striking — now the two sides have 100 days to come up with a deal

Workers walked out of King Soopers stores in the Denver metro area in February for nearly two-weeks until the grocer and the union set a 100-day peace deal to return to negotiations.

The peace deal expired after talks ended with limited progress.

But could workers from King Soopers go on strike again to join Safeway picketers? It’s not clear yet.

Cordova said in her video message that they’re waiting on guidance from the national UFCW organization on whether the Colorado chapter has to make its members vote again to authorize a strike against King Soopers or if they go straight to the picket lines.

“Once we get guidance, we will act accordingly,” Cordova said.