They say the county's current contract offer — a 6% raise over 30 months — would effectively result in less money in their members' pockets because of increasing health insurance premiums.

"We want the county to come to the table and really negotiate with us," said David Green, treasurer of SEIU 721, which represents 55,000 county employees. "The offer they put forward would essentially be a pay cut for our workers, who haven't had any salary increase in more than five years."

County officials counter that the union is describing a "worst-case scenario," saying that the county does not want to see employees' pay cut and that the medical premium is one bargaining chip on the table.

"That's a subject of negotiation, and they know that and we know that," said county Supervisor Zev Yaroslavsky. "They are postulating a scenario where they get nothing and we get everything. That's not what negotiating is about."

Tuesday morning, workers will be bused into downtown Los Angeles from workplaces throughout the county. Some have received permission for time off; others plan to walk off their jobs and could face discipline. Labor leaders project that 5,000 workers will kick off their "Day of Action" at California Plaza, then march to the Hall of Administration and hold a rally outside at about the time the county Board of Supervisors typically holds its weekly meeting.

That meeting was canceled Sept. 10, officials said, when supervisors realized they would not have a quorum. But SEIU work site organizer Norma Herrera called the cancellation "cowardly" and suggested that it was prompted by the labor dispute.

County officials said they did not expect services to be reduced as a result of the labor action, despite the fact that many of SEIU's members deal directly with the public in their jobs.

"The county has contingency plans in place to ensure critical public services remain," said county spokesman David Sommers.

It's unclear whether Tuesday's walkout would be a one-time event or is the first step in an escalation of tensions. Labor and county negotiators are expected to continue meeting in coming weeks. Representatives from the union's various bargaining units are expected to meet the second week of October at the Los Angeles Convention Center to debate accepting the county's latest offer or move toward declaring an impasse or a strike authorization vote. But the union faces pressure: Any raise its members receive will not be retroactive to the date of their old contract's expiration but will begin when a new one is ratified.

The dispute is a departure from recent years, when relations between labor and the county have been fairly good. The two groups banded together to weather the recession: Workers agreed to put off pay raises and cost-of-living increases for about five years, and the county avoided laying off or furloughing any workers, setting it apart from other California governmental agencies during the recession.

Elected officials and county bureaucrats have been effusive about the sacrifices workers made during those years, and they agree that with the economy showing signs of recovery, it is time to increase workers' pay. Several other bargaining groups have already agreed to the 6% raise package, but workers in SEIU 721 — the largest county labor union — say the county is not going far enough.

Assessor's office employee Monica Lopez, 47, said she plans to participate in Tuesday's action out of frustration : County workers who forwent raises need to be made whole, she said.

"When you've been hearing the same promises year after year and had no results, the frustration starts leading to resentment," the Montebello resident said.

In addition to seeking higher wages, the union is proposing to raise the so-called "living wage" paid to county contractors' employees, reduce the caseload of social workers, strengthen a ride-sharing program and close a property-tax loophole for large corporations.

Labor leaders hope the turnout and excitement at the planned rally will mirror "Rolling Thunder," an early 1990s series of protests and strikes that stopped deep wage cuts during a recession. But the likelihood of large numbers participating is questionable.

On Thursday, SEIU held a rally aimed at getting workers to participate in the Tuesday protest. It took place outside the Hall of Administration, where 1,200 local members work. At that time, fewer than 50 had signed up to participate and a similar number attended the rally, to the dismay of organizers.

"We walked these halls up and down — people know about today," Herrera told them. "On Oct. 1, this cannot be repeated. I don't care what you do, I don't care who you drag, you've got to get your co-workers out here."

seema.mehta@latimes.com