Credit and debit card fees were always a big business expense for Patti Riordan, who owns a hobby shop in Lancaster, Ohio. But, she said, since the coronavirus pandemic, they’ve become a pain point.

As a pandemic precaution, droves of customers gave up cash in favor of contactless payment methods like tap to pay, and the percentage of Ms. Riordan’s sales processed through a card network rose to 75 percent, up from 65 percent in 2020. Now, so-called swipe fees are her third biggest expense, behind payroll and rent, amounting to roughly $18,000 a year.

“There is no room to pay more — we’re just operating so thin,” Ms. Riordan said.

Debit and credit card fees are among the top monthly expenses for many small businesses, which say the costs are becoming more onerous as fewer consumers carry cash. Merchants of all sizes paid a total of $172 billion in processing fees in 2023, up from roughly $116 billion the year before the pandemic, according to the Nilson Report, which tracks the payments industry. That’s a 48 percent increase.

When they swipe a credit card, businesses pay fees to the bank that issues the card, to the payment network and, often, to companies like Toast and Square that help process the transaction. The biggest share of those fees — averaging more than 2 percent of a transaction amount — is set by payment networks like Visa and Mastercard and paid to the issuing bank, ultimately benefiting both the banks and the networks.

Visa and Mastercard together control more than 80 percent of the market for card purchases. But, the two companies have argued, there is robust competition among payment networks. American Express — which accounts for roughly 11 percent of card purchases, and Discover, roughly 2 percent — are the two other leading payment networks, according to Nilson Report data.

Merchants can’t negotiate their own fees, and they don’t always understand why the fees change.