US officials issued Thursday a record $300 million fine over a robocall scam that placed more than five billion unsolicited calls to targeted consumers over three months.

Operating under different names across multiple countries including Hungary, Panama and the United States since at least 2018, the enterprise executed an extraordinary number of unsolicited calls, including to numbers on the National Do Not Call Registry, the Federal Communications Commission said.

US officials had announced the proposed $300 million fine in December, giving the accused 30 days to response. When the FCC received no response, it announced Thursday's action.

If the parties do not pay the fine, the case will be referred to the Justice Department for collection, the FCC said.

The operation violated federal spoofing laws by using more than one million different caller ID numbers to trick people into answering the phone.

Key players in the scheme, which involved "the false and misleading claim of selling auto warranties," were Roy Cox, Jr. and Michael Aaron Jones, both of whom were under lifetime bans against making telemarketing calls following earlier government enforcement actions.

"We take seriously our responsibility to protect consumers and the integrity of US communications networks from the onslaught of these types of pernicious calls," said FCC Enforcement Bureau Chief Loyaan Egal.