The U.S. Justice Department on Tuesday sued Visa, the world’s biggest payments network, saying it propped up an illegal monopoly over debit payments by imposing “exclusionary” agreements on partners and smothering upstart firms.

Visa’s moves over the years have resulted in American consumers and merchants paying billions of dollars in additional fees, according to the DOJ, which filed a civil antitrust suit in New York for “monopolization” and other unlawful conduct.

“We allege that Visa has unlawfully amassed the power to extract fees that far exceed what it could charge in a competitive market,” Attorney General Merrick Garland said in a DOJ release.

“Merchants and banks pass along those costs to consumers, either by raising prices or reducing quality or service,” Garland said. “As a result, Visa’s unlawful conduct affects not just the price of one thing – but the price of nearly everything.”

Visa and its smaller rival MasterCard have surged in the past two decades, reaching a combined market cap of roughly $1 trillion, as consumers tapped credit and debit cards for store purchases and e-commerce instead of paper money. They are essentially toll collectors, shuffling payments between the merchants’ banks and cardholders.

More than 60% of debit transactions in the U.S. run over Visa rails, helping it charge more than $7 billion annually in processing fees, according to the DOJ complaint.

But the payment networks’ dominance has increasingly attracted attention from regulators and retailers.

In 2020, the DOJ filed an antitrust suit to block Visa from acquiring fintech company Plaid; the companies initially said they would fight the action, but soon abandoned the $5.3 billion takeover.

In March, Visa and Mastercard agreed to limit their fees and let merchants charge customers for using credit cards, a deal retailers said was worth $30 billion in savings over a half decade. A federal judge later rejected the settlement, saying the networks could afford to pay for a “substantially greater” deal.

“Visa wields its dominance, enormous scale, and centrality to the debit ecosystem to impose a web of exclusionary agreements on merchants and banks,” the DOJ said in its release. “These agreements penalize Visa’s customers who route transactions to a different debit network or alternative payment system.”

Furthermore, when faced with threats, Visa “engaged in a deliberate and reinforcing course of conduct to cut off competition and prevent rivals from gaining the scale, share, and data necessary to compete,” the DOJ said.

In February, credit card lender Capital One announced its acquisition of Discover Financial, a $35.3 billion deal predicated in part on Capital One’s ability to prop up Discover’s also-ran payments network, a distant No. 4 behind Visa, MasterCard and American Express.

Capital one said that once the deal is closed, it will switch all its debit card volume to Discover and a growing share of credit card volume over time.

 This story is developing. Please check back for updates.