On Friday, Visa confirmed that the company is being investigated by federal agencies. The Department of Justice has initiated a probe. It is checking whether the company used anticompetitive practices to remain at the top of the debit card market.

The Wall Street Journal reported the investigation by the DOJ and the company’s stocks fell by 6.2%. It closed at $206.90. According to sources familiar with the matter, the investigation is looking to see if Visa improperly blocks merchants from using rival payment networks for debit-card transactions. Rival networks often charge lower fees.

Merchants have complained about this from many years. When they have tried to use smaller networks like Shazam or NYCE with a card that bears the name of Visa or MasterCard, it cannot be used through these smaller networks. So, they have to pay higher transaction fees when compared with the smaller ones who charge less, according to the WSJ.

The feds are also looking to see if the incentive offered by Visa to banks encourages them not to route payments through other networks but to exclusively use the ones who give them larger incentives. This is also another aspect of the probe according to one source.

Two months ago, Visa had withdrawn from a $5.3 billion acquisition of Plaid because of the antitrust proceedings. In November, the DOJ had filed a lawsuit to stop the merger. The Justice Department allegedly said that this partnership was being put in place to stop a rival from ascending.

The Justice Department alleged that Visa CEO, Al Kelly had proposed merger as an “insurance policy.” to protect its U.S. debit-card business. Visa disagreed with this view and said that Plaid was not a competitor.

On Friday, the Department of Justice did not respond when ask for comments.

According to its annual report, Visa’s total payment volume was $8.9 trillion in 2019. This is almost double of MasterCard who is the second largest player in the market.