The European Commission fined Visa 10.2 million euros ($14.45 million) on Wednesday for refusing to let Morgan Stanley join its payment card system in Britain.
Visa refused to admit the U.S. bank from March 2000 to September 2006 without objective justification, the European Union's executive body said in a statement.
Brussels is trying to inject more competition into the sector.
"The payment cards industry plays a key role in the creation and functioning of the single market in payments," EU Competition Commissioner Neelie Kroes said.
"The Commission will not tolerate anticompetitive behavior and will intervene if companies are illegally refused membership of payment card networks," Kroes added.
Visa had said Morgan Stanley was a competitor, but the Commission dismissed this argument.
Visa reached a settlement with Morgan Stanley in September last year and admitted the U.S. bank as a member.
The Commission said it decided to impose a fine even though Morgan Stanley withdrew its complaint. The bank was excluded from the U.K. market for six and a half years, including more than two years after the Commission started action against Visa, the Commission said.