Employees at four Colorado Safeway locations went on strike Sunday, forming picket lines after negotiations between their union and the grocery store chain broke down.

The labor action, organized by United Food and Commercial Workers Local 7, began at 6 a.m. Sunday at stores in Estes Park, Fountain, Pueblo, and the Safeway Distribution Center in Denver. The union has authorized an Unfair Labor Practices strike, citing stalled negotiations and what it described as “numerous unfair labor practices” by the company.

“Albertsons and Safeway employees have had enough,” UFCW Local 7 President Kim Cordova said in a statement. “We gave the company multiple chances to avoid this labor dispute. Earlier this week, we offered the company a clear path to withdraw its concessionary proposals and instead fully fund healthcare benefits.”

Wage increases and understaffing remain key issues in the contract talks, which have been ongoing for more than nine months.

Photos posted on the UFCW Local 7 Facebook page showed dozens of striking employees outside the four locations Sunday morning. Cordova urged union members still working inside to join the picket line.

The union said additional Safeway stores may join the strike in the coming days. Targeted locations include:

• Metro Denver
• Boulder
• Broomfield
• Brighton
• Evergreen
• Idaho Springs
• Castle Rock
• Grand Junction
• Salida
• Parker
• Conifer Meat Plant

Fort Collins, Greeley, Longmont, and Loveland stores are expected to hold strike authorization votes soon. According to Cordova, 98% of voting union members have already backed a strike.

On Wednesday night, UFCW Local 7 issued Albertsons—Safeway’s parent company—a 72-hour notice to cancel a contract extension that had taken effect Sunday.

“Safeway in Colorado remains committed to productive discussions with UFCW Local 7,” Safeway officials said in a statement responding to the strike.

“We respect the rights of workers to engage in collective bargaining and are negotiating in good faith to achieve an agreement,” Safeway officials said.

“Our focus remains on providing exceptional service to our customers and fostering a positive working environment for our associates.”

The union is also in talks with King Soopers, though a no-strike agreement between the two sides expired recently. UFCW Local 7 has not announced whether it will strike at King Soopers but has indicated that putting pressure on one chain will spur movement at the other.

“United, we can get the company to stop its unfair labor practices and negotiate the fair contract that you deserve,” Cordova said in a message to Safeway workers.

Denver Gazette business reporter Bernadette Berdychowski contributed to this report.