Over 60% of the more than $4 trillion in debit transactions that take place in the U.S. every year are routed to Visa’s electronic payments network, Attorney General Merrick B. Garland said in a press conference Tuesday afternoon. The DOJ has alleged Visa uses that leverage to deploy a web of anticompetitive agreements that penalize merchants and banks for using competing payment networks.

The department also said Visa threatens market entrants with high fees if they do not cooperate. One Visa executive allegedly said the company had point-of-sale service Square, which also operates a digital wallet called Cash App, “on a short leash.”

“We allege that Visa has unlawfully amassed the power to extract fees that far exceed what it could charge in a competitive market,” Garland said. “Merchants and banks pass along those costs to consumers, either by raising prices or reducing quality or service. As a result, Visa’s unlawful conduct affects not just the price of one thing, but the price of nearly everything.”

Visa general counsel Julie Rottenberg called the lawsuit “meritless” and said the company would defend itself vigorously.

“Today’s lawsuit ignores the reality that Visa is just one of many competitors in a debit space that is growing, with entrants who are thriving,” she said in a statement. “When businesses and consumers choose Visa, it is because of our secure and reliable network, world-class fraud protection, and the value we provide. We are proud of the payments network we have built, the innovation we advance, and the economic opportunity we enable.”

Americans use debit cards more than any other payment method and over twice as much as credit cards, according to data from the Federal Reserve.  Younger and less affluent Americans often particularly rely on them, said Ben Mizer, the department’s principal deputy associate attorney general.

“When merchants raise their prices to cover Visa’s exorbitant fees,” he said, “the burden of Visa’s anti-competitive conduct falls disproportionately on Americans who are less well-off and who feel the impact of high prices most painfully.”

Biden Administration continues antitrust offensive

Visa and rival Mastercard, which last year settled a separate enforcement action brought by the U.S. Federal Trade Commission, have amassed a combined market cap of roughly $1 trillion. Both companies are the quintessential types of “middlemen” the DOJ has increasingly targeted in industries from real estate to health care. In May, the department and several states filed a suit seeking to break up Ticketmaster-parent Live Nation.

The Visa suit is also part of a broader antitrust offensive from the DOJ under President Biden, which has intensified in the final year of his term. The DOJ scored a historic victory in August when a federal judge ruled Google had illegally monopolized the search market, its first major antirust win over Big Tech in more than two decades.

The National Economic Council, which advises the president, did not directly comment on the lawsuit but touted the Biden administration’s commitment to ensuring “real competition.”

“This Administration has also taken on credit card late fees and banking overdraft fees,” Jon Donenberg, the council’s deputy director, said in a statement, “and will continue working to take on other unfair junk fees on everyday transactions.”

After Bloomberg first reported news of the suit against Visa on Monday, several analysts said investors shouldn’t panic. The case should take years to wind through the courts, they noted, if it even goes to trial.

Nonetheless, investors clearly didn’t cheer the news.

This story has been updated with statements from Visa and the National Economic Council.