Handsets made by ZTE and Nokia do not violate InterDigital Inc's patents for wireless phones, a U.S. International Trade Commission judge said in a preliminary ruling. The full commission is expected to issue a final ruling in October.

InterDigital shares plunged more than 10 percent on the ruling, and but they recovered somewhat and were down about 7.3 percent in late-afternoon U.S. trading. InterDigital said in a statement that it would appeal to the full commission, and potentially to the US Court of Appeals for the Federal Circuit.

The company sued Samsung Electronics and Huawei for infringement but these two companies paid it to go away. The company accused the companies of infringing on seven patents when the case was filed in 2013, but four dropped out in the course of litigation.

The ITC is a popular place for patent lawsuits because it can ban products that infringe on patents from being imported into the United States which makes it good leverage to get a company which will not pay up back to the negotiating table.