The European Commission has accused Apple of abusing its market position for contactless smartphone payments.
In a preliminary finding, it said the US company may have broken competition law by preventing rivals from accessing its "tap and go" technology.
Apple denies the charge and has promised to engage with the Commission.
If the charges are upheld, it could be fined up to 10% of its global turnover of $36.6bn (£29.2bn) based on its revenue last year.
"We have indications that Apple restricted third-party access to key technology necessary to develop rival mobile wallet solutions on Apple's devices," EU Vice-President Margrethe Vestager said in a statement.
"We preliminarily found that Apple may have restricted competition, to the benefit of its own solution Apple Pay," the EU official who is in charge of competition policy said.
Less innovation= less choice
According to the Commission, this behaviour from Apple has an "exclusionary effect" on competitors and "leads to less innovation and less choice for consumers for mobile wallets on iPhones".
In response, the tech giant said its payment system was only one of many options available to European consumers.
It added that it had "ensured equal access" to mobile payment technology, while "setting industry-leading standards" for privacy and security.
"We designed Apple Pay to provide an easy and secure way for users to digitally present their existing payment cards and for banks and other financial institutions to offer contactless payments for their customers," the company said in a statement.
"We will continue to engage with the Commission to ensure European consumers have access to the payment option of their choice in a safe and secure environment."
However, the EU antitrust regulators said their investigation had not found "any evidence" that would point to a more open design posing a "higher security risk".
"On the contrary, evidence on our file indicates that Apple's conduct cannot be justified by security concerns," Ms Vestager said.
The Commission also accused Apple anti-competitive practices dating back to 2015 when it launched Apple Pay.
More than 2,500 banks in Europe use Apple Pay and Apple smartphones represent around a third of the market across Europe. Next year, the EU plans to implement new rules for technology firms, detailed in its Digital Markets Act.
EU regulators also charged Apple last year, accusing the firm of distorting competition in music streaming markets after rival company Spotify lodged a complaint.