DENVER (NewsNation Now) — Thousands of King Soopers workers in Colorado went on strike Wednesday for better pay.

The strike started at 5 a.m. following unsuccessful back-and-forth negotiations between Kroger-owned King Soopers, the largest grocery store chain in Colorado, and the United Food and Commercial Workers Local 7.

The union representing more than 8,700 King Soopers supermarket workers rejected the Colorado chain’s increased wage offer, setting the stage for a three-week strike.

On Tuesday, King Soopers had sweetened a wage offer to workers of UFCW Local 7 to $170 million, calling it their “last, best and final offer.”

This came after the union last week rejected several previous offers, including a $148 million investment in wages and signing bonuses over three years.

“The company’s last, best, and final offer, in many ways, is worse than its previous offers,” Kim Cordova, president of UFCW Local 7, said in a statement.

King Soopers and City Market released a statement calling the decision by the UFCW Local 7 to strike “reckless and self-serving, without regard for the implications to associates and Coloradans.”

Cordova said the company’s wage offer “still doesn’t cut it” and retains many of its previously proposed concessions and adds new concessionary items.

The union is seeking an increase in wages of at least $6 per hour for all workers.

However, the company’s “last, best and final offer” proposed raises of up to $4.50 per hour based on job classification and tenure, which was the same as its previous proposal.

King Soopers said stores will remain open during the strike.

Reuters and NewsNation affiliate KDVR contributed to this report.