Some drivers would love to have a cellphone-free bubble around their cars, but when a Florida man allegedly created one every day on his commute, it didn’t necessarily make the highway a safer place.

Jason R. Humphreys of Seffner, Florida, operated a cellphone jammer in his Toyota Highlander sport-utility vehicle during his daily commute for as long as two years before the U.S. Federal Communications Commission and the local sheriff tracked him down, the FCC said on Tuesday. Now he’s facing $48,000 in fines, with 30 days to pay or file a response.

Humphreys told the FCC he used the jammer to keep people from talking on their cellphones while driving. Talking on a cellphone while driving is legal in Florida, even without a hands-free kit, though texting while driving is banned. Using a cellphone jammer is illegal for everyone but federal law enforcement, regardless of intent, according to the FCC.

Not only do jammers prevent consumers from making emergency calls, but they can disrupt critical communications by safety agencies, the FCC said. Hillsborough County sheriff’s deputies confirmed that firsthand when they pulled Humphreys over. They said their two-way portable radios lost contact with the dispatcher as they got close to the SUV.

It was Metro PCS, the regional mobile operator now owned by T-Mobile USA, that tipped off the FCC that something seemed to be wrong on a stretch of Interstate 4 between Seffner and downtown Tampa about 12 miles away. On April 29, 2013, Metro PCS reported that its cell towers along the route had been experiencing interference during the morning and evening commutes. The FCC investigated with direction-finding techniques and found strong wideband emissions coming from a blue Highlander.

FCC agents and sheriff’s deputies pulled the SUV over, talked to Humphreys and searched the vehicle, where they found the jammer behind a seat cover on the backseat, the FCC said. Humphreys allegedly told the FCC he had been using the jammer during his commute for the past 16 to 24 months. Later testing found that the device could jam cell signals in three bands.

Humphreys is charged with unauthorized operation of a jammer, use of an illegal device and causing intentional interference. The FCC imposed the maximum fine for one violation of each, which adds up to $48,000. Because Humphreys used the jammer for so long, the fine could have been as high as $337,000, the FCC said.

Humphreys could not immediately be reached at a phone number listed for him and he did not return a message.

Despite some calls to legalize cellphone jammers in certain settings, the FCC takes a hard line on the devices, which are illegal to manufacture, sell or import in the U.S.