(Reuters) – Visa is under investigation by the Department of Justice over allegedly charging retailers more for not using the payment firm’s proprietary “tokenization” technolgy, Bloomberg News reported, citing people familiar with the matter.

Shares of Visa (NYSE:V) were down 1.06%, at $237.29 in premarket trading.

The technology swaps sensitive card numbers with tokens that can be exclusively used on a particular device or with a merchant, the report said.

DOJ’s probe of Visa began in early 2021 and is investigating if the credit card company uses anti-competitive practices in the debit card market.

Visa and the DOJ did not immediately respond to a Reuters request for comment.