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.

Unionized King Soopers workers in Broomfield, Boulder and Louisville will join their fellow United Food and Commercial Workers Local 7 members from around the Denver metro area in a two-week strike beginning at 5 a.