Callers posing as tax and immigration agents have threatened Americans with arrest, deportation or other punishments unless they sent money to clear up deportation warrants or unpaid income taxes.
The US government says it's a scam that's tricked at least 15,000 people into shelling out more than $US300 million ($A395 million).
In a first-of-its kind takedown, the Justice Department has announced charges against 61 defendants in the United States and abroad in connection with the call centre operations based in India.
As agents fanned out across the country to make arrests, officials in Washington advised the public that the callers on the other end of the line are fraudsters and not representatives of the US government.
"The US government does not operate in this manner," said Assistant Lawyer General Leslie Caldwell, head of the Justice Department's criminal division.
"We never call to demand that money be loaded immediately onto prepaid cards. US government agencies do not call to demand immediate payments to avoid deportation or to avoid arrest."
The indictment, which was issued by a federal grand jury last week in Houston, charges the defendants - which include five call centres in India - with crimes including wire fraud, money laundering and false impersonation of an officer of the United States.
Authorities served warrants in cities around the US on Thursday and were seeking the extradition of defendants in India, Caldwell said.
The indictment outlines a complex web of criminal actors, each with a different role in the conspiracy.
Callers working off of scripts and posing as officials with the Internal Revenue Service and US Immigration and Customs Enforcement would tell unsuspecting victims on the other end of the line that they had failed to pay taxes they owed or were at risk of deportation, and that a fast payment was needed to get them out of trouble.
Data brokers arranged the purchase of names and personal information of potential targets.
"Runners" in the US were responsible for getting scammed funds into bank accounts, a laundering process aided through wire transfers and prepaid debit cards. And payment processors based in India helped facilitate overseas payments.
Though the calls would appear to be obviously bogus, officials say savvy and successful individuals have nonetheless been duped.
The callers would use information about their victims they learned through the Internet to present a facade of authenticity, and the numbers that appeared on a caller ID often seemed to come from a legitimate US government call centre.
The Justice Department said it's not clear that the victims will get any of their money back, or that the defendants arrested cannot be easily replaced.
