Intriguingly, the letter from Dimon appears to be a warning to Barclays. In his missive, Dimon expresses a hope that JP Morgan and Barclays can have an "honest and forthright discussion about what we might do to resolve our differences". But he then goes on to raise the issue of Barclays' alleged courtroom mis-statement in a way that can only be interpreted as a shot across the British bank's bows.