The UAW is pushing back against General Motors' announcement last week that put the fate of five plants and thousands of workers in North America up in the air.

Terry Dittes, UAW vice president and director of the union's GM Department, said in a letter Monday to the Detroit automaker's head of labor relations that the company had violated commitments during 2015 contract bargaining.

At issue was the company's use of the wording in the company's announcement, when it said the plants, including Detroit-Hamtramck Assembly and Warren Transmission, "will be unallocated in 2019."

The letter from Dittes to Scott Sandefur said that using the term "unallocated" rather than closed or idled does not relieve the company of its obligations and asks that the company rescind its decision. Dittes wrote that he was disappointed that GM had chosen to ignore a history of resolving job security and product commitments during bargaining, which gets underway next year.

The letter referenced a document attached to the contract called "Plant Closing and Sale Moratorium" that was signed by Catherine Clegg, who was then GM's vice president of North American Manufacturing and Labor relations but is now in a new role.

"As a result of your deep concern about job security in our negotiations and the many discussions which took place over it, this will confirm that during the term of the new collective bargaining agreement, the company will not close, idle, nor partially or wholly

sell, spin-off, split-off, consolidate or otherwise dispose of in any form, any plant, asset, or business unit of any type, beyond those which have already been identified, constituting a bargaining unit under the agreement," according to the document.

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That moratorium does provide an out in the event conditions change that are "beyond the control of the company," but given the proactive nature of GM's announcement, it's unlikely the union would see this in that light.

In a statement about the letter to GM, UAW President Gary Jones said the union has "been clear that the UAW will leave no stone unturned and use any and all resources available to us regarding the future of these plants."

In last week's announcement, GM CEO and President Mary Barra said the company would see $6 billion in cost savings and was restructuring for a changing market.

“The actions we are taking today continue our transformation to be highly agile, resilient and profitable, while giving us the flexibility to invest in the future,” Barra said in a news release.

Contact Eric D. Lawrence: elawrence@freepress.com. Follow him on Twitter: @_ericdlawrence.