The US Department of Justice (DOJ) filed a civil antitrust lawsuit Thursday to block credit card giant Visa’s acquisition of Plaid.

According to the DOJ, Visa is a “monopolist in online debit services, charging consumers and merchants billions of dollars in fees each year to process online payments.” Plaid is a “successful fintech firm” that allegedly “is developing a payments platform that would challenge Visa’s monopoly.” This platform is called pay-by-bank and allows consumers to pay online using their bank details, rather than their debit card details. Pay-by-bank is “already widely available in other countries.”

Plaid earned approximately $100 million in 2019. Visa sought to acquire Plaid for $5.3 billion. The DOJ’s complaint alleges that Visa’s CEO wanted to acquire Plaid to protect against a “threat to our important US debit business” and that Visa “must always do what it takes to protect [its] business.”

The DOJ claims that the acquisition of Plaid would unlawfully maintain Visa’s monopoly and deprive merchants and consumers of competition that would “drastically lower costs for online debit transactions.” The DOJ further claims that by eliminating competition, the acquisition would “likely reduce quality, service, choice, and innovation.”

The DOJ requests that the US District Court for the Northern District of California permanently block the acquisition and declare such acquisition to be unlawful.