(NewsNation) — The Federal Communications Commission on Thursday issued a nearly $300 million fine for a robocall scam made by the largest illegal robocall operation the agency has ever investigated.

The record fine hits an international network of companies who the FCC says made more than five billion robocalls about car warranties to more than 500 million phone numbers in just three months in 2021.

The FCC says the companies violated federal statutes, FCC regulations and federal spoofing laws by using more than one million different caller IDs to try to trick people into answering the phone. The companies are also accused of dialing numbers on the National Do Not Call Registry, making pre-recorded voice calls and failing to give a call-back number so people could block them.

The FCC says the enterprise has operated the complex scheme “designed to facilitate the sale of vehicle service contracts under the false and misleading claim of selling auto warranties” since at least 2018.

The scammers reportedly did business as Sumco Panama, Virtual Telecom, Davis Telecom, Geist Telecom, Fugle Telecom, Tech Direct, Mobi Telecom and Posting Express. The FCC says two of the operation’s key players, Roy Cox and Aaron Jones, were under lifetime bans against making telemarketing calls following lawsuits by the FCC and state of Texas.

“We take seriously our responsibility to protect consumers and the integrity of U.S. communications networks from the onslaught of these types of pernicious calls,” FCC Enforcement Bureau Chief Loyaan A. Egal said in a news release.

In an attempt to stop the scheme in its tracks, the FCC directed all U.S.-based voice service providers to stop carrying traffic associated with certain companies involved. As a result, the FCC says the illegal auto warranty robocalls dropped by 99%.

If the companies do not “promptly” pay the $299,997,000 fine, the case will be referred to the Department of Justice.