About 27,000 machinists employed by Boeing, including at least about 5,000 in the south King County area, are on strike after negotiations between their union and the company ended last week without a new three-year contract proposal to present to the union membership.

Pickets were out in force Monday at the plant for the 737 airliner in Renton. Monday was considered the first day of the strike, even though it was called for 12:01 a.m. last Saturday. Pickets also went up at Boeing plants in Everett, Oregon and Wichita, Kan., with early indications that the strike would continue indefinitely.

According to strikers on the picket line in Renton, many workers wanted to hold up their signs the previous week. However, union leaders asked that they hold off because the negotiations were continuing in Florida.

So when the strike began officially, many union members, including Steve Averill, a precision rework specialist in Renton who has worked for Boeing for about 20 years, decided to take what Averill called a 48-hour hiatus.

“We were ready to strike” Sept. 4 and 5, Averill said. “The workers were pretty well-organized.”

During that 48-hour period, the company, the union and a federal mediator “worked hard in pursuing good-faith explorations of options that could lead to an agreement. Unfortunately, the differences were too great to close,” said Scott Carson, president of Boeing Commercial Airplanes.

The members of the International Association of Machinists and Aerospace Workers (IAM) earlier had voted 87 percent to go on strike and 83 percent to reject a proposed contract.

Connie Kelliher, a union spokeswoman, acknowledged that some workers were ready to hit the picket lines a week earlier. But she said there were still plenty of workers on the picket lines last weekend.

“There was a faction of members upset by the 48-hour delay,” she said. But the goal of a strike vote, she added, is to bring the company back to the negotiating table.

By mid-week, there were no reports of progress in negotiations.

For the machinists, the biggest concern in the agreement is the number of “takeaways” in the contract proposal, related to such key employee issues as promotions, sub-contracting and benefits, Kelliher said. “Boeing wordsmithed this to death, changing one word here and one word there.”

Another big issue for workers is job security, she said.

The strike has stopped production of the 737 at the sprawling Renton plant, idling about 5,000 striking machinists. The union represents production workers there.

Non-machinists union members are continuing to work. Unions representing Boeing workers agree in their contracts that they won’t honor the picket lines of other striking unions.

Boeing spokesman Tim Healy called the Boeing offer the “best in the aerospace industry.” He said the company doesn’t agree the contract is filled with “takeaways.”

“We are talking about a contract that would put $34,000 in the pocket of the average machinist over the next three years,” he said.

But the term “average worker,” based on pay, doesn’t sit well with some Boeing workers. The average pay for employees is about $54,000, but Kelliher said many, including maintenance workers, “are lucky to reach $20,000.”

Company officials said other Boeing operations in Washington, Oregon and Kansas would continue despite the IAM strike, but the company doesn’t intend to assemble airplanes during the strike.

During the work stoppage, Boeing will support its customers and its planes that are in service, company officials said. The company will continue delivering planes that were completed prior to the strike and keep providing customers with spare parts.

The IAM is among the nation’s largest industrial trade unions, representing over 700,000 working and retired members in the airline, aerospace, manufacturing, railroad, woodworking and shipbuilding industries.