Office of Fair Trading Investigates Visa's Exclusive Olympic Deal
Sports fans who want to buy tickets by card for the London 2012 Olympics will only be able to use the Visa payments system.
The restrictions are part of the sponsorship deal struck between Visa and the Olympic and Paralympic Games.
Visa credit and debit cards will be the only ones accepted at shops or cash machines at Olympic venues.
The competition enforcer the Office of Fair Trading said it was looking into the matter.