WASHINGTON, July 30 -- For the Chinese manufacturers who have spent years building the world's most advanced humanoid robots and solar inverters, Tuesday was the day Washington finally decided they were not welcome. The Federal Communications Commission announced a ban on new imports of foreign-made humanoid robots, four-legged robot dogs and power inverters, warning that the devices, predominantly those made in China, could be used for surveillance or remote cyberattacks against the United States. The announcement's security rationale was sweeping. The supporting evidence was not.

FCC Chair Brendan Carr, whom the Trump administration elevated to lead the commission, framed the action as a necessary response to what the agency called "un...