UAW Local 551 Communications posted early Thursday that 1,778 of 2,317 total workers voted against the proposed deal, while 539 agreed to it after two days of voting.
The contract included a $6,000 signing bonus and profit-sharing checks in lieu of annual raises, but a potential sticking point may have been pay for new hires. New employees would be paid less than existing employees to keep costs down.
Mayor Rahm Emanuel last week quickly celebrated the tentative deal after Ford announced its agreement with United Auto Workers to create 2,000 jobs between Illinois' two plants.
But Gov. Pat Quinn on Thursday said he warned last week it may be too early to celebrate, since the union still had to ratify the deal.
Quinn remained confident in a positive outcome. Still, he said, the process should be respected.
"I believe in workplace democracy," he said. "Workers have a right to look at the agreement and see if they want to ratify it."
Ford said in a statement the company believes the agreement "is fair to our employees and improves Ford's competitiveness in the U.S. We remain optimistic that the tentative agreement will be approved."
Workers represented by Local 558 at the Ford metal stamping facility in Chicago Heights vote Thursday.
Local 551 isn't the first union to vote down the proposed contract. Workers at Ford's assembly plants in Wayne, Mich. also rejected the deal, according to Crain's Chicago Business.
A strike could be on the horizon if the agreement isn't ratified, union leaders said.