Navistar, which was sued by Ford in January for allegedly failing to live up to its contract, says it has not been paid for the truck engines since the lawsuit was filed, The Chicago Tribune reports.

Those engines are used in about 70 percent of Ford's heavy-duty trucks, which account for 40 percent of the automaker's full-size pickup-truck sales.

Ford's lawsuit, filed in a Michigan court, accuses Navistar of "unjustifiably" raising prices on its diesel engine used in Ford's F-Series line, the top-selling U.S. pickup for 25 years, and of breaking a warranty cost-sharing agreement.

Ford withheld the money it owes Navistar to cover what it says is Navistar's portion of those costs.

The clash threatens Ford's Super Duty pickup production, which the company is counting on to help return it to profitability, the Tribune said.

A Ford spokeswoman says the automaker has enough engines to continue building the trucks in the "near term."