One day in June, seven months after the US imposed stiff tariffs on plywood from China, a wood importer in Oregon got a call from a supplier asking if he would like to get some Chinese plywood tariff-free. How would that work, asked importer David Visse. …“Don’t worry about it,” the supplier told him. The plywood would be stripped of its Chinese markings, and “we’ll ship it under some other code.” …The business of code-fudging is expanding in step with tariff increases, undermining US efforts to shield American business from foreign competition, according to importers, customs officials, trade attorneys and shipping brokers. As trade conflict grows between the two largest economies, these professionals say, code misclassification is starting to compete with transshipment—the rerouting of goods through third countries—as a way to duck tariffs. …The Chinese government forbids false customs declarations. …US customs authorities say they haven’t always received full cooperation from China. (full story available to Wall Street Journal subscribers only)