King Soopers, a chain owned by Kroger, with 121 stores in Colorado and Wyoming, has been negotiating a new contract with the union since October.

Some 10,000 grocery store workers across the greater Denver area went on strike Thursday, claiming unfair and illegal negotiating practices by King Soopers while their union has been negotiating a new contract with the store chain.

On their second strike in three years, workers say Kroger-owned King Soopers engaged in unfair labor practices during contract negotiations.