Giacomo and Vincenzo Russo claim Watford dismissed them as directors "without any justification".
The Barclays Premiership club revealed this week that the brothers, who had been on the board at Vicarage Road since 2004, had been removed from their position "with immediate effect".
In a joint statement, the brothers said: "Our concerns have been and remain the best interests of Watford Football Club and its supporters.
"Our removal from the board is completely contrary to out wishes and without any justification whatsoever.
"We have been long-term supporters financially and generally of the club. It comes as a complete shock that the board should see fit to take this act on at such a critical stage in the club's history."
Giacomo - known as Jimmy - is the founder of food suppliers Valley Grown Salads, of which Vincenzo - known as Vince - is a director.
The brothers also have business interests in Egypt, Spain and Israel.
A statement from Watford chairman Graham Simpson read: "On behalf of the board, I would like to express our gratitude to Giacomo and Vincenzo Russo for their contribution to Watford Leisure (the holding company of Watford FC) and their commitment to the football club during their tenure."