The U.S. Justice Department plans to allege that Visa Inc. illegally monopolized the U.S. debit card market, according to people familiar with the matter.

The antitrust division is set to file a lawsuit as soon as Tuesday accusing the operator of the largest U.S. payments network of a range of anticompetitive conduct, said the people, who asked not to be identified discussing the case. The government is expected to file the case in federal court.

Antitrust enforcers are preparing to accuse Visa of taking steps to keep rivals from challenging its dominance in the debit card market, said the people. The government’s allegations include that Visa made exclusive agreements to hinder the expansion of competing networks and thwarted efforts by technology companies to enter the market.

Visa shares fell as much as 1.95% in post-market trading in New York on Monday after the news.

Visa and the Justice Department declined to comment.

The Justice Department lawsuit would be the culmination of years-long probes of Visa’s business practices. The investigation was born out of the firm’s failed acquisition of the financial-technology infrastructure firm Plaid Inc. in 2021.

Over the course of the inquiry, the Justice Department also examined Visa’s pricing structure in what’s known in the industry as “tokenization” technology.

Payments network rival Mastercard Inc. settled a separate enforcement action last year targeting its tokenization technology practices brought by the U.S. Federal Trade Commission, which also enforces antitrust laws.

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