From CNN:
China has threatened to slap sanctions on American companies that sell arms to its rival Taiwan as part of a range of punitive actions Beijing is taking to protest the deal.
I'm not sure what sanctions they have in mind, but it's hard to imagine this resulting in a WTO complaint even if there were a possible violation. The U.S. is usually on the other side of such concerns, and they are unlikely to want this kind of issue adjudicated at the WTO.
