Contract negotiations between the Defense Department and Lockheed Martin that involve continuing work on the F-35 joint strike fighter have hit a snag. National Defense Magazine reported that the dispute hinges upon a $6.1-billion “unilateral” contract the Pentagon awarded to Lockheed. Under the contract, the manufacturer would be required to continue building F-35s – even in cases such as this, where the two parties have not agreed on a price. Lockheed could appeal the Defense Department action to the Armed Services Board of Contract Appeals or the U.S. Court of Federal Claims, National Defense reported.