Ford worker opposition to concessions agreed by the United Auto Workers appears to be growing.

UAW-represented workers had rejected concessions at six plants by Tuesday night, threatening to vote down a deal to give the automaker cost parity with General Motors and Chrysler, Reuters reported.

Though urged by UAW national leaders to ratify the agreement, shop floor workers have objected to giving Ford the same kind of 'no-strike' pledge on wages and benefits the union gave GM and Chrysler in bankruptcy.

Workers in Flat Rock, Michigan, Kansas City, Missouri, and plants in Livonia, Sterling Heights, Canton and Ypsilanti have all rejected the agreement.

Workers at five other UAW plants supported the tentative pact last week, Reuters noted.

The tentative agreement announced on 13 October includes production commitments from Ford intended to protect jobs and a one-time US$1,000 bonus for workers.

The news agency noted if Ford workers ultimately rejected the agreement, they also would be rejecting pattern bargaining that has ruled financial negotiations with the Detroit-based automakers.

Ford has said agreements GM and Chrysler made with the UAW around their government supported bankruptcy reorganisations would put the company at a disadvantage over the long term.

Voting ends on Friday at a UAW branch which represents several thousand workers at multiple Ford facilities, including the Dearborn truck assembly plant where leaders have voiced opposition to the givebacks.