Wisconsin Knife Works v. National Metal Crafters

Wisconsin Knife (plaintiff) sent NMC (defendant) six purchase orders, each barring modification except by a signed writing; NMC signed acknowledgments (with delivery dates) for the first two but only orally provided delivery dates for the remaining four, then missed those oral deadlines. Wisconsin Knife terminated the contract and sued for breach; NMC argued the delivery dates weren't firm and that Wisconsin Knife had orally agreed to extend them. The jury was instructed to decide whether the contract had been modified, found that it had and that the modified contract wasn't breached, and the trial court dismissed Wisconsin Knife's complaint.

Whether, under the Uniform Commercial Code, a contract prohibiting modification except by a signed writing can be orally modified if the oral modification is detrimentally relied upon.