Dozens of retailers are seeking to void nearly $6 billion of U.S. antitrust settlements with Visa Inc (V.N), MasterCard Inc (MA.N) and American Express Co (AXP.N) after learning that opposing lawyers exchanged confidential information, potentially tainting the accords. A group of retailers filed papers that remain under seal in the Brooklyn, New York federal court to scuttle their $5.7 billion accord with Visa and MasterCard, which won court approval in 2013, the retailers’ lawyer Owen Glist said in an email.