Wells Fargo, one of the world’s biggest banks, just got caught in an elaborate scheme charging customers for bank accounts they never signed up for.

CNN Money reported Thursday afternoon that the bank fired approximately 5,300 employees who opened an estimated 1.5 million unauthorized bank accounts and cards. Customers charged for those accounts were never notified of their existence. The Consumer Financial Protection Bureau (CFPB) announced it would fine the bank $100 million for the scam — the largest fine the agency has ever imposed. Workers were incentivized to scam customers in order to net year-end bonuses.

“The Bank had compensation programs for its employees that encouraged them to sign up existing clients for deposit accounts, credit cards, debit cards, and online banking,” the CFPB wrote on its website. “According to today’s enforcement action, thousands of Wells Fargo employees illegally enrolled consumers in these products and services without their knowledge or consent in order to obtain financial compensation for meeting sales targets.”

According to the CFPB, accounts were maintained by Wells Fargo employees secretly moving customers’ money from existing accounts into the phony accounts, and then subsequently charging those customers for having insufficient funds in their original accounts.

Credit card accounts opened by Wells Fargo employees without customers’ consent also resulted in annual fees, in addition to interest charges and late fees. CNN Money reported that bank employees submitted 565,443 applications for credit cards on customers’ behalf without their knowledge or consent, dating back to 2011.

“We regret and take responsibility for any instances where customers may have received a product that they did not request,” Wells Fargo said in a public statement.

In addition to the $100 million fine levied by the CFPB, Wells Fargo may have to end up paying up to $85 million in additional fines and penalties, as well as an estimated $5 million in refunds to customers who were scammed.