Before there was the class action, the US Justice Department sued. Visa and MasterCard settled.[1] The settlement required those companies to allow merchants to "steer" customers to less expensive cards with with discounts and incentives. Not that this agreement didn't override state laws which prohibit that practice. AMEX choose to go to trial, lost, and the case is currently on appeal at the Second Circuit (the judgment stayed).[2]

The class action lawsuit was settled in principle back in 2012 and approved by the district court in 2013, but was thrown out recently by the Second Circuit.[3] It would have been the largest class action settlement in history, but many large merchants objected to being bound by a settlement that they had no part in negotiating.

[1] http://www.lexology.com/library/detail.aspx?g=a2722e0c-e0a6-...

[2] http://www.reuters.com/article/us-american-express-antitrust...

[3]http://www.wsj.com/articles/visa-mastercard-class-action-set...