Federal judge rules against American Express in closely watched antitrust suit

A judge has ruled that American Express violated U.S. antitrust laws by barring merchants from asking customers to prefer one credit card over another.

U.S. District Judge Nicholas Garaufis said in his ruling that American Express' nondisclosure policies harmed competition and prevented merchants from trying to lower their credit card processing costs. He also ruled that AmEx's policies deliberately kept consumers unaware how much using their cards cost merchants each time they use it.

The case was a major blow to AmEx, who argued that its policies kept it competitive against the larger payment networks Visa and MasterCard.

American Express, in a statement, said it was disappointed with the decision and will appeal.

American Express shares fell 2 percent in midday trading following the ruling.