US Federal Communications Commission (FCC) proposed to impose a fine of $299,997,000 on “the largest robocall firm” it has ever investigated. It will be the largest fine in the FCC’s history and targets a firm that made more than 5 billion calls in three months, enough to “call every person in the United States 15 times.”

The operation is run by Roy Cox Jr. and Michael Aaron Jones through their Panamanian company Sumco, as well as other companies. In July of this year, the FCC issued its first-ever “K4 Notice” and “N2 Order,” requiring all US telephone carriers to stop transmitting traffic related to car warranty scams.

“This resulted in a massive, 99 percent drop in the volume of such calls since June, according to RoboKiller (spam blocking programs),” the FCC wrote.

The FCC proposed its largest-ever fine because it found the robocallers met the criteria for “egregious violations.” Consumers described the calls as “incessant” and “harassment,” and the robocallers used dirty practices like calling health care workers from spoofed hospital numbers. The firm also violated multiple FCC rules, like failing to identify the caller at the start of a message.

In the calls, a message would open with something like “we’ve been trying to reach you concerning your car’s extended warranty,” and prompt you to speak to a scam “warranty specialist.” Robokiller advises users to avoid the calls in the first place if possible, not follow prompts, and above all, never provide personal information like banking details.