Mastercard has been fined €570.6m by the European Commission for breaching EU anti-trust regulation.
The Commission said the card giant was guilty of obstructing merchants' access to cross-border card payment services.
This limited possibility for merchants to benefit from better conditions offered by banks established elsewhere in the single market, breaching competition law.
Commissioner Margrethe Vestager said: "European consumers use payment cards every day, when they buy food or clothes or make purchases online.
"By preventing merchants from shopping around for better conditions offered by banks in other member states, Mastercard's rules artificially raised the costs of card payments, harming consumers and retailers in the EU."
The Commission found that, because of Mastercard's rules, retailers paid more in bank services to receive card payments than if they had been free to shop around for lower-priced offers.
It led to higher prices for retailers and consumers, to limited cross-border competition and to an artificial segmentation of the Single Market.
For its part, Mastercard co-operated with the Commission by acknowledging the infringements of EU competition rules and was therefore granted a 10% reduction in the fine.
The firm said: "This decision relates to historic practices only, covers a limited period of time of less than two years and will not require any modification of Mastercard's current business practices.
"Mastercard sees the closure of this anti-trust chapter as an important milestone for the company."