Two ranking JPMorgan Chase & Co directors issued a letter to shareholders on Friday arguing against recommendations by proxy advisory firms to split the duties of Chairman and CEO Jamie Dimon and vote against some directors.

The board is unanimous in its view that it is best for Dimon to hold both roles and that the current governance structure "is working effectively," according to the letter signed by presiding director Lee Raymond and William Weldon, who is chairman of the corporate governance and nominating committee.

The letter warned that a vote against current directors or to split the CEO and chairman roles "could be disruptive to the company and is not in shareholders' best interests."

(Reporting By David Henry in New York; writing by Lauren Tara LaCapra; Editing by Gerald E. McCormick)