Visa Inc. and Mastercard Inc. fees are under fresh scrutiny from European Union antitrust enforcers, less than a decade after a series of probes ended with hefty fines and an agreement to cut some of their controversial levies.

European Commission regulators last week circulated a new series of questions to market participants on “scheme fees” they impose on the financial institutions that provide card-payment services to retailers using Visa and Mastercard networks, according to people familiar with the matter.

The questionnaires homed in on whether retailers have a choice of whether to accept Visa and Mastercard payments, whether merchants are getting value for money from the fees eventually passed on to them, and how transparent the charges are, said the people, who spoke on condition of anonymity.

While at an early stage, it’s possible the EU’s competition watchdog could move toward opening of a formal probe, ramping up the risk of heavy fines of as much as 10% of annual revenue if firms are found to have abused their market dominance.

The fresh scrutiny comes on the heels of comments from European Central Bank President Christine Lagarde that the 27-member bloc needs to reduce its dependence on foreign payment providers. Lagarde has pitched the rollout of a digital euro currency as the best way of bolstering sovereignty and lowering vulnerabilities.

The EU commission in Brussels declined to comment on specifics “as the investigation is ongoing.” It said it “has a number of investigative powers at its disposal, including the sending of requests for information.”

San Francisco-based Visa said its fees “reflect the immense value that we provide to financial institutions, merchants and consumers in Europe.” It said “this includes extremely high levels of security and fraud prevention, near-perfect operational resilience and reliability.”

Purchase, New York-based Mastercard said “is focused on enabling commerce around the world” and that it “offers consumers and businesses choice, ways to pay and be paid that are hassle-free and worry-free, secure and most convenient for them.”

Visa and Mastercard have both found themselves in the crosshairs of global antitrust enforcers for years.

In 2019, the EU slapped Mastercard with a €570.6 million ($646 million) penalty for imposing rules that regulators said may have artificially raised the costs of card payments in the region. Later that year, regulators also signed off on a pact with Visa and Mastercard that that required them to reduce fees for foreigners shopping in the region.

Last year a US federal judge rejected a $30 billion settlement that Visa and rival Mastercard had reached earlier in the year with American merchants in an attempt to resolve two decades of litigation over credit-swipe fees.