Negotiations are reaching a critical stage at Boeing Co., where last month workers — members of the International Association of Machinists and Aerospace Workers — authorized a strike. The union represents more than 24,000 workers in the Puget Sound area in Washington, and in Gresham, Oregon, and Wichita, Kansas.

The existing contract expires Sept. 3. The Machinists struck for 28 days before ratifying that contract.

Around the clock bargaining begins at SeaTac on Friday, Aug. 22.

A “Final Countdown Rally” is slated for 12:30 p.m. on Sunday, Aug. 24, at the Doubletree Hotel in SeaTac.

Union officials said the strike authorization vote, held July 16, passed by a 99 percent margin.

“The vote sends a strong message that ‘It’s Our Time This Time,’ ” said Machinists District 751 President Tom Wroblewski.

“It’s Our Time This Time” is the theme of the union’s bargaining campaign.

The strike sanction vote in Washington was held at Key Arena in Seattle. In Oregon, Boeing employees met at the football stadium at Mt. Hood Community College in Gresham.

The Machinists Union says that over the past five years Boeing’s after-tax profits exceeded $13 billion — up over 828 percent.

During that time, airplane orders also have skyrocketed — increasing by more than 560 percent and setting a record in 2007 with 1,413 orders.

“All this means Boeing is one of the most successful companies in the world and that ‘It’s Our Time This Time’ to make improvements in all areas of the contract,” Wroblewski said.

Voting on the contract will take place on Sept. 3. If a majority accept the contract, negotiations end and the contract is signed. If a majority reject the contract, but less than two-thirds of the membership vote to strike, the contract is automatically accepted by default. No strike can be called. (This happened in 2002.) If a majority vote to reject the contract, and more than two-thirds vote to strike, a strike can be called at 12:01 a.m. Sept. 4.