The Department of Justice (DOJ) is suing to block Visa’s acquisition of Plaid, citing concerns over Visa’s monopoly in the online payments market.

Plaid is a service that allows users to securely connect their bank accounts with the finance apps they use. This allows them to send and receive money, as well as interact with their accounts.

Given Visa’s stranglehold on the debit and online payments market, Plaid could be seen as competition and threat to Visa’s business. In fact, according to the DOJ, Visa’s CEO saw the acquisition of Plaid as an “insurance policy” and a way to protect against a “threat to our important US debit business.”

That threat has come into clear focus as Plaid has been planning a service that would more directly compete with Visa. Although the new service has yet to be released, it is believed to be an online debit service, one that would directly challenge Visa’s dominance.

Visa’s attempt to buy a potential competitor, to the tune of $5.3 billion, is not going over well with the DOJ.

“American consumers and business owners increasingly buy and sell goods and services online, and Visa – a monopolist in online debit services – has extracted billions of dollars from those transactions,” said Assistant Attorney General Makan Delrahim of the Justice Department’s Antitrust Division. “Now, Visa is attempting to acquire Plaid, a nascent competitor developing a disruptive, lower-cost option for online debit payments. If allowed to proceed, the acquisition would deprive American merchants and consumers of this innovative alternative to Visa and increase entry barriers for future innovators.”