The U.S. Supreme Court on Monday agreed to decide an 11-state antitrust challenge to American Express Co.'s merchant rules, a case that the U.S. Justice Department litigated with the states for more than six years and then abandoned at the high court's door.

In Ohio v. American Express, the states argue that American Express Co. is violating antitrust laws through rules that contractually bar merchants from encouraging customers to use other credit cards that charge lower prices to businesses.

The Justice Department and the states had sued American Express over the rules in 2010 in federal district court in New York. The district court held that the government proved the anti-steering rules were anti-competitive because they stifled competition among credit card companies. The trial judge also found that American Express failed to prove pro-competitive benefits from its rules.