A ruling that Visa and Mastercard had violated antitrust law has been upheld by the US Supreme Court.
Rules had prevented banks from issuing rival cards
The case stemmed from a 1998 Justice Department lawsuit challenging the credit card issuers' regulations.
The groups appealed after a court found they were wrong to block US banks from issuing credit cards on rival networks such as Discover and American Express.
Discover card owner Morgan Stanley has said it would be seeking undisclosed damages from the two firms.
It has long complained the rules were anti-competitive and had locked it out of the fast-growing debit card business.
The Supreme Court decision is also expected to benefit issuers such as MBNA, which announced in January it would be issuing American Express cards.
A federal judge in New York originally ruled against Visa and Mastercard in 2001.
The credit card groups appealed to the Supreme Court when an appeals court upheld that decision.