Mastercard's £700m deal for Vocalink has raised concerns over competition in the payments infrastructure business with the market watchdog.
Owned by a collective of 18 banks, including Barclays, Santander, Lloyds, Royal Bank of Scotland and HSBC, Vocalink provides the infrastructure for many payments in Britain such as Bacs and the Faster Payments Service as well as the Link ATM network.
Concerns have been raised with the Competition and Markets Authority (CMA) that Mastercard's ownership would reduce competition in these areas.
It said Mastercard and Vocalink were two of the UK's three "most credible" infrastructure providers in payments, and "As such, the merger would reduce the number of bidders and limit the ability of the Link scheme to obtain good value when tendering for an infrastructure provider". It did not find the concerns over Bacs and FPS warranted.
Mastercard has been asked to suggest remedies to the ATM competition concerns or faces an in-depth investigation over the deal.
Mastercard said it will address the issue before the 11 January deadline.
"We’re pleased to have the opportunity to address their one concern, regarding the Link ATM scheme, in the timeframe provided," it said in a statement.
"This acquisition promises to bring greater choice and innovation to the payment ecosystem, enabling people, governments and businesses to pay the way they want to pay."
Mastercard snapped up a majority stake in the company for £700m in July last year, with a further £169m potential earn out, giving a windfall to the banks and they plan to retain a 7.6 per cent stake for at least three years.
The banks were forced to sell off the business, which governs £6 trillion of payments such as bank transfers, direct debits and salary payments across the country every year, by the the Payments System Regulator over competition concerns.