The Supreme Court (search) on Monday let stand a ruling that the Visa and MasterCard credit card associations violated federal antitrust law by barring their member banks from issuing credit and charge cards on the rival networks of American Express Co. (AXP) and Morgan Stanley. (MWD).

Without any comment, the justices rejected separate appeals by Visa and MasterCard of a ruling that found their so-called exclusionary rules harmed competition.

The two appeals stemmed from a lawsuit brought in 1998 by the Justice Department (search) over the membership rules by Visa and MasterCard, which operate as joint ventures owned by their member banking institutions.

A federal judge in New York ruled in 2001 that the rules were unlawful and ordered Visa and MasterCard to repeal them and to not adopt any similar policy in the future. A U.S. appeals court last year upheld that decision.

Visa and MasterCard, which have argued that their rules do not hurt competition, appealed to the Supreme Court.

Visa's attorneys said the case will have "extremely broad practical consequences for U.S. companies and consumers." They added, "The necessary effect of invalidating Visa's loyalty rule will not be to lower prices for consumers."

MasterCard's attorneys said the appeals court ruling "will undermine the incentives for vigorous competition that have produced compelling consumer benefits in an industry of fundamental importance to the economy."

The Justice Department opposed the appeals and said the appeals court ruling did not present any legal issue warranting Supreme Court review.