WASHINGTON — The Supreme Court handed American Express a win Monday in a lawsuit over rules it imposes on merchants who accept its cards.

Under their contracts, merchants who accept American Express generally can’t encourage customers to use other credit cards, even though they charge merchants lower fees. The federal government and a group of states sued over those so-called “anti-steering” provisions, arguing that they violate federal law.

But on Monday the high court ruled 5-4 in favor of American Express.

“In this case, we must decide whether Amex’s antisteering provisions violate federal antitrust law. We conclude they do not,” Justice Clarence Thomas wrote in an opinion for himself and his conservative colleagues, Chief Justice John Roberts and Justices Anthony Kennedy, Samuel Alito and Neil Gorsuch.

American Express cheered the ruling in a statement after it was announced.

“The Supreme Court’s decision is a major victory for consumers and for American Express. It will help to promote competition and innovation in the payments industry,” the statement said.

The case the Supreme Court ruled in dates to 2010 when the Obama administration and more than a dozen states sued American Express along with Visa and MasterCard, which had similar anti-steering rules. Visa and MasterCard agreed to change their practices. American Express, which accounts for about a quarter of the credit card market, decided to go to trial.

A federal trial court judge initially ruled against American Express, finding that its rules stifled competition among credit card networks and led to higher fees for merchants and higher prices for consumers. An appeals court reversed the decision, ruling for American Express. The Supreme Court upheld that decision.

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