When Comcast designed a mobile app for its cable customers to schedule DVR recordings over the Internet, the company likely had no idea they would end up violating a federal importation law. But that's just what a federal trade agency determined late last year when it blocked all imports of Comcast's cable boxes because the mobile app infringed on a patent. And if the U.S. International Trade Commission gets its way, a lot more American companies could be forced to defend themselves from a trade agency— even when their business involves no foreign trade.

The ITC is charged with investigating and blocking importation of goods that infringe on U.S. patents. Of course, as its name indicates, the ITC is a trade agency, and so the commission only investigates accusations against importers. If it finds imports do indeed infringe on a U.S. patent, the agency issues an exclusion order barring the infringing product from entering the country.

Comcast, however, doesn't import anything or conduct any cross-border trade. It buys cable boxes from domestic suppliers and uses the boxes to provide services to domestic customers. Those cable boxes are just regular cable boxes— they don't infringe any patents. So how did Comcast end up violating a trade law?