A new report has found that American shoppers pay millions in fees when they receive “cash back” at major retail stores.

The Consumer Financial Protection Bureau (CFPB) report surveyed eight major retailers (Dollar General, Dollar Tree/Family Dollar, Kroger, Albertsons, Walgreens, CVS, Walmart and Target) and evaluated their practices for charging cash back fees on purchases made with debit or prepaid cards.

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Three of the retailers in the sample (Dollar General, Dollar Tree/Family Dollar and Kroger) collected over $90 million in cashback fees annually, the report said.

The CFPB also estimated that the marginal cost to merchants in processing each transaction is likely to be just a few cents, compared to the much higher fees retailers charge consumers per transaction.

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At Dollar General and Dollar Tree/Family Dollar, cash back fees for small withdrawal amounts are the highest in the sample ($1 fee or more for cash back amounts under $50). Kroger, the nation’s largest grocery chain, recently announced new fees at their Harris Teeter stores (75 cents for $100 cash back or less) and charges an additional 50 cents for up to $100 cash back at their other branded stores such as Ralph’s, Fred Meyer and others.

The report also found that consumers with lower incomes or fewer banking options pay disproportionately high cash-back fees. Dollar stores are often located in small rural towns, communities of color and low-income communities – areas where there are also fewer bank branches and more residents rely on cash for their daily transactions, the report said.

“While Dollar General is not a financial institution, it offers cash back options in our more than 20,000 stores nationwide as a service to customers who may not have convenient access to their primary financial institution,” Dollar General said in a statement. “These services can also help customers save on fees compared to alternative, non-retail options such as check cashing locations or ATM fees.”

“Like many retailers, Dollar Tree and Family Dollar offer cash back as a convenient service to our customers,” said a Dollar Tree company spokesperson. “Shoppers who wish to take advantage of our cash back offer will be charged a clearly stated fee, which in turn helps offset the various costs we incur in offering this helpful service.”

A representative for Kroger did not respond to a request for comment in time for publication of this story.

Many merchants set withdrawal amounts for a single transaction in advance, typically between $5 and $50. Adding a fee for small transactions can be a significant percentage of the withdrawal amount and can also lead to repeated withdrawals, with consumers being charged a new fee each time, the CFPB said.

“While retail chains have long offered free cash back on debit card purchases, the CFPB has found that dollar store chains and other retailers are now charging fees for accessing cash,” said CFPB Director Rohit Chopra. “Many people in small towns no longer have access to a local bank where they can withdraw money from their account for free. This has created a playing field for retailers to charge fees for cash back.”

Established in 2011 as part of the Dodd-Frank Wall Street Reform and Consumer Protection Act, the Consumer Financial Protection Bureau is a U.S. government agency that works to ensure that consumers are treated fairly by banks, lenders, and other financial institutions.