Fiat Chrysler Automobiles is cutting the third shift at its Windsor Assembly Plant beginning June 29.
The automaker says it notified Unifor Thursday about the change that will affect about 1,500 employees.
The move keeps the shift operational for an additional three months. Originally scheduled to shut down last September, the shift's closing was given a four-month reprieve in November to last until March 31.
FCA says it made the decision to match volumes with demand as production of the Dodge Grand Caravan is phased out at the end of May.
"The company will make every effort to place indefinitely laid off hourly employees in open full-time positions as they become available based on seniority and will offer retirement packages to eligible employees,'' spokeswoman LouAnn Gosselin wrote in an email.
Unifor Local 444 president Dave Cassidy held a news conference in Windsor to discuss the impact.
"We worked to prevent this shift loss with the full understanding of the devastating affect that this would have on our membership," he said in a news release.
"Now we will ensure that these workers receive the support that they need in this process as we continue to fight for new product for Windsor Assembly with the goal of preserving and increasing these good paying auto manufacturing jobs."
The decision will lead to significant job loss in the parts supply chain, and inflict damage to both the local and national economy, the national union said in a statement.
"Unifor is very disappointed that FCA was unable to find a solution that would have avoided job losses," said national president Jerry Dias. "There is no question that the economic ramifications will be felt across the region and throughout the country."
He said investment in Canadian automobile production will be a priority during negotiations that get underway this summer with FCA, General Motors and Ford. It will also continue to press various levels of government about the need for a national auto strategy to stabilize and grow the sector.
The plant, which produces the Chrysler Pacifica and its hybrid version, as well as the Dodge Grand Caravan, has about 6,100 employees.
FCA announced last year that it would invest US$4.5 billion in Michigan to build a new assembly plant and upgrade other operations and create 6,500 jobs in the process.
The planned cut in Windsor will come about six months after General Motors ended production at its assembly plant in Oshawa, Ont., at a loss of about 2,600 unionized workers.