Contract talks between King Soopers and United Food and Commercial Workers union Local 7 heated up Wednesday after the labor group sued in federal court, alleging the grocery chain violated its contract by using cleaning contractors to stock shelves.

The lawsuit came as the Denver-based King Soopers proposed to increase worker wages $145 million over four years as part of a new contract with Local 7’s 17,000 employees.

The contract expires Jan. 8. King Soopers said in a news release that its offer would increase hourly wages for 75% of employees to more than $18 and more than half would earn more than $20 an hour.

In addition to the lawsuit, Local 7 president Kim Cordova accused King Soopers of releasing portions of a contract proposal to the media and employees while sharing a different proposal with the union.

In doing so, Cordova said via email, King Soopers omitted key concessions that union employees would have to make to receive the wage increase. Those include higher employee health care premiums and reduced benefits; a requirement that employees work more hours to receive health care coverage; an OK for the company to hire so-called gig workers or independent contractors; and limits on workers’ ability to earn overtime.

Cordova said the union rejected the offer.

“While we continue trying to negotiate in good faith with King Soopers, this move was meant only to deceive the press, employees, and customers in a failed effort to hide the truth that the company cares more about profits than workers,” Cordova said.

In an earlier news release, Cordova said King Soopers is combating a labor shortage by using staffing services Retail Odyssey and Day Ready/People Ready to stock shelves in several Denver area stores rather than “offering current and prospective workers a competitive wage rate sufficient to attract new workers.”

King Soopers said Wednesday via email that it’s disappointed the union sued instead of following grievance and arbitration processes outlined in the contract.

The union said in its release that the staffing services are paying wages starting at $16 an hour, which it said is far higher than many grocery employees are paid.

The lawsuit alleges Local 7 discovered in late November that King Soopers was using employees from the two staffing services to stock shelves and refrigerated foods, in violation of the contract. Local 7 has filed four grievances with King Soopers over the alleged contract violations at stores in Golden, Greenwood Village and Lakewood, which the company has denied.

The union’s contract with King Soopers bars the company from contracting out operations in its stores, except for sanitation and floor maintenance. Vendors who deliver merchandise such as beverages and cookies directly to the company’s stores are allowed to stock that merchandise.

Local 7 demanded King Soopers stop using the contracted employees to stock shelves and has sought arbitration about the alleged practice. The suit said cases typically take more than a year to reach arbitration. As a result, the union is seeking a court order to stop the alleged practice until the matter can go to arbitration.

The lawsuit provides a window into the negotiations — it includes letters between Cordova and Athar Bilgrami, division human resources leader for King Soopers and City Market, as an exhibit. The letters show King Soopers has offered to boost starting wages from $12.35 to $13.50 in northern and southern Colorado and to $14 in the Denver area but doesn’t include increases for City Market employees.

The union is seeking a $6 an hour increase for King Soopers and City Market employees.

King Soopers and City Market are owned by Cincinnati-based grocery giant Kroger.

The union also is negotiating with Safeway; that contract also expires Jan. 8.