The Canadian Auto Workers union calls the move a “devastating blow” to the 1,100 workers who have been out of work for at least two years.
When the plant closed in 2009, 300 workers were handed pink slips, in addition to 800 who were already on lay off at the time.
The Illinois-based company says production in Chatham has already been absorbed by Navistar plants elsewhere.
Navistar says it also plans to scale back operations at its headquarters and motor coach manufacturing plant in Oregon.
One of its subsidiaries is also closing a plant in Indiana.
The CAW says the Chatham plant was in the community for more than 60 years, and had been one of the largest employers in the area.