United Auto Workers president Bob King has instructed union local branches representing Ford plants to hold their rank-and-file strike authorisation vote by 2 September, intensifying pressure on the automaker to reach a new labour deal before its existing contract expires.

The call for the vote, a standard negotiating practice, was outlined when King addressed about 150 union officials in Chicago, the Wall Street Journal.

Union membership approval would allow the UAW to initiate a strike if it fails to reach a new labour agreement with Ford once the current contract expires on 14 September. A UAW spokeswoman told the WSJ the vote was a routine move.

Ford is the most vulnerable of the Detroit Three automakers since it is the only US-based auto maker without a no-strike agreement with the union. The UAW agreed to no-strike terms as part of the bankruptcy reorganisation of GM and Chrysler.

Ford’s recent strong profits, combined with chief executive Alan Mulally’s 2010 pay package of US$26.5m, has made Ford a target for the union, which had agreed to a variety of concessions, including a two-tier system that lowered wages to $14 an hour for new hires.

King said he is hopeful of reaching a new deal with all three Detroit automakers by 14 September although he gave no specifics on the state of negotiations, people familiar with the matter said.

“We are committed to working together to reach an agreement that’s beneficial to both parties,” said Ford spokeswoman Marcey Evans. A UAW spokesperson could not be reached for comment.

King may attempt to resolve the outstanding grievance between Ford and the UAW during the contract talks, the WSJ sources said. The UAW claimed Ford violated its current labour contract when it reinstated merit increases for salaried workers last year. The UAW had hoped the issue would be settled by an arbitrator before contract talks began last month.

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