The Supreme Court ruled in favor of American Express today in the case American Express Co. v. Italian Colors Restaurant.
The court voted five to three, and was split along party lines. Justice Sonya Sotomayor recused herself from the decision.
The ruling means merchants must use arbitration to file claims, or one by one, making them unable to file class action together against the company in the case of a dispute. The merchants that filed claims didn't want to accept American Express debit, credit or charge cards.
As expected, Twitter's been a hotbed for speaking out against the court's pro-business ruling.