Barclays was fined 8.4 million pounds (U.S. $10.2 million) for failing to provide retailers with complete information about the costs of the card services it supplied, which prevented them from shopping around for cheaper deals and passing the benefits onto customers.

The U.K.’s Payment Systems Regulator (PSR), which oversees methods of bank transfer, announced its findings Thursday that Barclays did not provide retailers with transaction information required under Article 12 of the EU Interchange Fee Regulation 2015/751. As a result, retailers were unable to easily understand the transaction fees associated with accepting certain types of card payments.

Since Barclays did not properly inform retailers about how fees were calculated or structured, or even how much they were being charged, they could not compare the bank’s charges with other card services providers to find cheaper deals or negotiate better terms with Barclays, according to the regulator.