The U.S. Justice Department has filed an antitrust lawsuit against Visa, alleging that the financial services behemoth uses its size and dominance to stifle competition in the debit card market, costing consumers and businesses billions of dollars.

The complaint filed Tuesday says Visa penalizes merchants and banks who don’t use Visa’s own payment processing technology to process debit transactions, even though alternatives exist. Visa earns an incremental fee from every transaction processed on its network.

According to the DOJ’s complaint, 60% of debit transactions in the United States run on Visa’s debit network, allowing it to charge over $7 billion in fees each year for processing those transactions.