By Foo Yun Chee

BRUSSELS (Reuters) -EU antitrust regulators have widened their investigation into Visa and Mastercard's fees as they seek feedback from terminal providers and payments companies that could lead to charges of anti-competitive practices, according to a European Commission document seen by Reuters.

A new questionnaire was sent after a similar one was distributed to retailers and merchants last month. The EU competition enforcer's scrutiny started in September as a result of complaints from merchants and payments companies about Visa and Mastercard's fees.

The two companies, which charge scheme fees for services related to participation in their card system, process about two-thirds of card payments in the euro zone.

The latest questionnaire asked about the number of fees or services charged by the two companies between 2017-2024, the number of new fees or services introduced, and the number of changes.

Regulators also wanted to know which scheme and processing services are mandatory, and how Visa and Mastercard inform payments companies about new fees or changes to existing fees.

The questionnaire asked if information provided by the two companies is sufficiently clear and if they give sufficient notice about changes to fees and services.

Respondents are also asked whether they have complained to Visa and Mastercard in the last seven years and how long it has taken to process the grievances.

"Mastercard offers consumers and businesses choice, ways to pay and be paid that are hassle-free and worry-free, secure and most convenient for them," a Mastercard spokesperson said.

Visa, meanwhile, said its fees reflected the value it provides to financial institutions, merchants and consumers in Europe. "This includes extremely high levels of security and fraud prevention, near-perfect operational resilience and reliability."

The questionnaire focuses on the degree to which the schemes must be accepted by all payment service providers and how they have raised fees in recent years, said a person familiar with the matter.

"This shift suggests that the Commission may be exploring ways to establish that Visa and Mastercard hold a dominant market position and are potentially abusing that dominance," the person said.

The Commission did not immediately respond to a request for comment.

The deadline for replies is June 2. Bloomberg first reported on the questionnaire.

(Reporting by Foo Yun Chee; Editing by Kirsten Donovan)