NEW DELHI (AP) – Indian police have arrested 70 people and are questioning hundreds more after uncovering a massive scam to cheat thousands of Americans out of millions of dollars by posing as U.S. tax authorities and demanding unpaid taxes, a police officer said Thursday.

According to police in Mumbai, the yearlong scam involved running fake call centers which sent voice mail messages telling U.S. nationals to call back because they owed back taxes.

Those who called back and believed the threats would fork out thousands of dollars to “settle” their case, Mumbai police officer Parag Marere said Thursday.

The scam brought in more than $150,000 a day, Marere said without giving a total sum. If the scam netted that amount daily, it would have made almost $55 million in one year.

Some victims were also told to buy gift vouchers from various companies, and hand over the voucher ID numbers which the impostors then used to make purchases, Marere said.

Police said they are likely to file charges against many of the 600 or more people still being questioned on suspicion of running the fake call centers, housed on several stories of a Mumbai office building.

Those arrested so far include several of the alleged ringleaders, as well as people accused of providing equipment and setting up the fake call centers. The criminal charges filed against the suspects include extortion, impersonation and violations of India’s information technology laws.

“We are questioning those who were involved in the fraud, including those posing as tax investigators,” Marere said.

Police raided the offices this week and seized hundreds of hard disks, hard disks, high-end servers and other electronic equipment.

Indian media reports said 70 percent of the scam’s proceeds were retained by the suspects in India, while the rest was paid to collaborators in the U.S.

Indian news broadcaster NDTV reported that one U.S.-based company allegedly collected the victims’ personal information and passed it to the fake call centers.

The IRS reports receiving more than 900,000 complaints about similar scam calls since October 2013. More than 5,000 people have fallen for the scam, paying out more than $26 million collectively as a result of scams.

The IRS has yet to comment on this recent arrest in India.

The IRS warns it will never call and demand immediate payment. It will never require you to use a specific payment method for your taxes, like a gift card or prepaid debit card. The agency will never ask for credit card numbers over the phone.

If you receive a call from someone claiming to be from the IRS and asking for money, you should never give out personal information. Report the call to the IRS using their “IRS Impersonation Scam Reporting” web page. You can also call 800-366-4484.