The US Department of Justice is investigating Visa's policies for charging retailer more for not using its proprietary tokenisation technology, according to Bloomberg.
The probe comes over two years after the DoJ's antitrust arm began looking into whether Visa has restricted the ability of merchants to send debit transactions through less expensive networks.
Several months ago, the Justice Department resolved another tokenisation case with Visa rival Mastercard.
Introduced by Visa nine years ago, tokenisation is designed to protect cardholder information by replacing the 16-digit account number with a token that only the payments giant can unlock.
The company offers merchants a lower price if they use it. According to Bloomberg, from April firms that impose recurring payments will pay $1.38 in card fees for every $100 in purchases they process on a traditional Visa card. If they use the tokenisation technology, they will only pay $1.28.