Seattle ? Members of The Boeing Co.’s largest union on Tuesday took the first step toward a possible strike if negotiations for a new contract fail this summer.

Members voting in three districts of the Machinists union in the Puget Sound area, Wichita and Portland, Ore. approved a strike authorization by a 98 percent margin, union officials said. The union, which represents 26,100 production workers at Boeing plants in the three states, did not give vote totals or say how many members cast ballots.

Members of Boeing's Machinists Union rally in Seattle to support a vote to authorize a strike. Members approved a strike authorization Tuesday by a 98 percent margin, union officials said.

The vote, to give negotiators authority to seek a strike, is largely a show of strength as the union continues talks with Boeing to replace a contract that expires at midnight Sept. 1. A strike only could occur if members reject what Boeing describes as a “best and final” offer expected in late August, and vote to strike by a two-thirds majority.

Tuesday’s vote also ensures that members can collect strike benefits from the international union.

“Your individual presence and our collective vote today is going to send a strong and emphatic message” to Boeing executives, who “just kind of hate it when we do it this way,” said Mark Blondin, president of Seattle-based Machinists District 751, the largest of the three districts that voted.

Boeing was expecting the results, said spokesman Chuck Cadena.

“A ‘yes’ vote is not an indication of the status of negotiations or a prediction of the outcome,” he said. “The Boeing team is approaching these negotiations as a collaborative effort and with the commitment to do everything possible and within reason to have a successful outcome.”

The union’s ranks have thinned due to layoffs numbering in the tens of thousands. Membership in District 751 has fallen about 25 percent since Sept. 11 and by almost half from the 1999 contract negotiations to fewer than 20,000 members.

Machinists also represent 5,000 workers in Kansas and 1,100 in Portland. Boeing and the union opened contract negotiations June 25 in Wichita. Round-the-clock negotiations begin Aug. 15.