CORRECTION: This story has been updated to correct an error about what the impasse declarations mean.

Riverside County declared an impasse Wednesday, Aug. 30, with two labor unions after more than a year of contract negotiations, escalating an increasingly acrimonious process affecting thousands of county employees.

The county notified Service Employees International Union Local 721 and Laborers’ International Union of North America Local 777 of the impasse Wednesday in letters to the unions’ negotiators. The impasse declaration sets up a round of fact-finding and mediation that could lead to further negotiations or the county imposing contract terms on union members.

SEIU, which represents more than 7,000 employees in the county’s health system, social services and other departments, issued a strike notice Tuesday in a boisterous protest that briefly disrupted the county Board of Supervisors meeting. Members picketed inside and outside the County Administrative Center afterward.

SEIU 721 President Bob Schoonover blasted the impasse in an emailed statement.

“Riverside County’s premature declaration of impasse certifies that they’ve never had a sincere interest in negotiating in good faith with their frontline workers,” Schoonover said, noting the union has filed 19 labor law complaints against the county.

He accused the county of giving SEIU the run-around on information the union requested about the county finances. He also said the county harassed employees who spoke out about unsafe working conditions at county medical facilities.

“Riverside County officials have shown a blatant disregard for labor laws, and frontline workers and residents deserve better,” Schoonover added.

SEIU’s strike is set to begin at 12:01 a.m. Sept. 6. It’s not immediately clear how county services would be affected, although county spokesman Ray Smith has said the county will make sure all departments are adequately staffed to protect public safety and that the county may go to court to prevent critical personnel from striking.

LIUNA Business Manager Stephen Switzer did not return a message seeking comment. But in an online post Tuesday on the union’s website, he wrote LIUNA would not declare a strike before the county declared an impasse.

“Going on strike is a very serious undertaking, which requires a great deal of sacrifice from the membership,” Switzer wrote. “Accordingly, we will not ask you to engage in strike activity unless we truly believe there is no other way to get a deal done.”

The county also has been in talks with the Riverside Sheriffs’ Association, which represents law enforcement personnel. Union President Robert Masson said membership has rejected a tentative deal with the county.

Contracts with LIUNA, SEIU and the union representing sheriff’s deputies expired last year. County officials have insisted on minimal raises for union members, citing an ongoing struggle to keep pace with new, ongoing and mandatory expenses that are outpacing revenue growth.

Unions have said the county wants to turn back the clock on members’ gains and balance the budget on employees’ backs. SEIU has been particularly aggressive in challenging the county, questioning supervisors’ spending decisions, including more than $40 million for a consulting firm to overhaul how county government functions.

SEIU also has accused the county of not doing enough to protect employees from being assaulted by patients at the county hospital in Moreno Valley and a Hemet mental health clinic.

Smith has said that since 2012 – the last time the county and the unions agreed to contracts – the average LIUNA and SEIU employees saw their salaries go up about 38 percent; sheriff’s union members saw an average increase of 30 percent, he said. That doesn’t include cost-of-living raises of 8 to 9 percent, Smith added