The contract expired today.
In Indiana, International employs 570 UAW workers at an engine assembly plant and 400 at a foundry operation in Indianapolis.
Both plants, which are located at 5565 Brookville Road on the east side, stopped production at midnight, said International spokesman Roy Wiley. However, the shutdown is not related to the labor contract, but instead was necessary because Ford is selling fewer pickup trucks with the diesel engine operation.
International also operates a truck engineering facility in Fort Wayne, although it was not immediately clear how many UAW employees work at the site.
International human resources vice president Jeff Bowen said in a statement, "At this point, we feel it's in everyone's best interest to keep talking and see if we can close the gaps that remain."