The European Union has warned that it may take action to increase competition in the credit card industry.
Visa and Mastercard dominate the credit card industry
EU internal market commissioner Charlie McCreevy said he was studying the industry, which is dominated by US firms Visa and Mastercard.
Mr McCreevy said the EU had powers to intervene if it found that competition abuse was taking place.
His comments come as EU officials prepare to probe competition allegations surrounding Mastercard.
A closed hearing of EU regulators on Tuesday will study allegations that the firm has been restricting competition by setting minimum fees retailers must pay for transactions made using its cards.
MasterCard associate general counsel Carl Munson declined to comment on the case, but said the company's business practices were helpful to those involved.
"We would argue that in the long run this is a benefit not just to cardholders but to merchants," he said.
Addressing a financial industry conference, Mr McCreevy said he was working closely with EU Competition Commissioner Neelie Kroes.
"I can assure you that the subject is also being very closely followed by national competition authorities," Mr McCreevy said.
"If there is abuse in the cards market then we have the instruments to intervene and we shall not hesitate to make use of our powers.
"We welcome alliances and cooperation that can produce more competition."