If you’re thinking of using a phone-jamming device to shut up your fellow motorists and get them off their phones while driving, think again: the Federal Communications Commission could hit you with fines, and could fine the company that sold you the gadget as well.

The FCC says in a pair of announcements today that it’s taken actions against a driver it first busted two years ago [PDF] as well as a Chinese company for marketing and selling signal jamming devices to U.S. consumers [PDF].

In the case of the driver, the FCC says that a Florida motorist was caught using a cell-phone jamming device in his car during his daily work commute back in 2014. The FCC says his “illegal operation” of the jammer continued for two years, causing interference to cell service along Interstate 4. His jamming also disrupted police communications, the FCC said when announcing a $48,000 fine against the man.

“This case highlights the danger posed to public safety by use of a single signal jamming device, which can disrupt all wireless and public safety communications in the area,” said Travis LeBlanc, Enforcement Bureau Chief. “These devices may not be used by the public under any circumstances.”

C.T.S. Technology didn’t get off quite so easily: the FCC slapped the Chinese electronics company with a $34.9 million fine for making and selling signal jammers.

According to the FCC, the company marketed the devices to U.S. customers through its own websites as well as third-party vendors. Included on the list of illicit jammers: small, concealable devices to block cell phone or GPS signals for a radius of a few yards, as well as high-powered jammers that could jam up a wide range of communications systems for several blocks.

C.T.S.’s website falsely claimed that the jammers were FCC-approved, and advertised shipping to the U.S., the FCC says. After an investigation by the agency’s enforcement bureau, the Commission proposed a $34,912,500 fine against C.T.S. Technology for its marketing of 285 jammer models in the U.S., and ordered it to ensure that its marketing complied with federal law.

The company didn’t respond to the proposed fine, formally known as a Notice of Apparent Liability for Forfeiture, but has since taken steps to bring its marketing into compliance with U.S. law, the FCC notes. However, since the Commission did not receive any evidence from C.T.S. Technology to contradict its findings, today’s decision, formally a Forfeiture Order, affirms the full proposed fine against the company.

“In today’s mobile world, cellular, GPS, and other signal jamming devices seriously jeopardize communications, business operations, and public safety,” LeBlanc said. “Marketing or selling these devices to the public is unlawful and comes with substantial penalties.”

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