Newstalk has learned that a deal agreed before Christmas to avert an ESB strike may be about to unravel. Widespread industrial action was avoided when the firm resolved a dispute over how the pension fund of the ESB was accounted for.

The ESB board is meeting today to sign off on its 2013 accounts. These are expected to show the largest-ever profit for a semi-state company of €600 million profits.

It is understood there are serious divisions at board-level over these financial statements.

Lawyers for the ESB Group of Unions has written to the Chairman and Chief Executive - Pat O'Doherty and Lochlann Quinn - threatening legal action over how the pension scheme is treated in the 2013 accounts.

Unions argue that ESB is responsible for any deficit in the pension but management are denying this.

Newstalk's Political editor Shane Coleman has seen the legal letter sent to management, and gave the details to Breakfast.