It's been a tough month for American Express and now a new federal judge's ruling may be another blow. American Express is our chart of the day. The fees that Amex charges merchants are routinely higher than those of other credit card companies. So some retailers have resorted to measures such as asking if customers had another form of payment such as Visa or Mastercard when a customer offers to pay with American Express. Amex cracked down on such behavior by saying merchants can't do that. A federal judge has now ruled that ----- violates United States antitrust laws. The judge hasn't issued a solution yet. Amex says it will appeal. Last week, it announced that its partnerships with JetBlue and the retailer Costco would be ending. Amex was the only card that Costco accepted beyond debit cards. A one year chart of Amex reveals that American Express stock has suffered. Shares slipped almost 2 percent after the announcement of Thursday’s ruling.