The FBI is warning other law enforcement agencies about the possibility that thieves may use GPS jammers to block the tracking of cargo shipments they are attempting to steal. In a "Private Industry Notification" bulletin not meant for public consumption but published on the website Public Intelligence, the FBI warns:

Since at least February 2012, various law enforcement and private sector partners have reported that GPS tracking devices have been jammed by criminals engaged in nefarious activity including cargo theft and illicit shipping of goods. Although banned by federal law, the jammers are readily available over the Internet and easy to employ.

Presumably the FBI also worries that suspected drug dealers, Muslims, political activists, and other common targets of government spying might deploy these cheap, widely available pieces of surveillance-defeating technology. According to the FBI, the devices cost $14 online but using them is illegal in the United States.