The publication of the letter late on Sunday comes just days after the Spanish government's disciplinary committee for sports (TAD) suspended tennis federation (RFET) president Jose Luis Escanuela for one month for failing to collaborate in a probe into the organisation's finances.
The letter blasted "the lack of transparency" in the distribution of the federation's revenues in the seven-point statement which was penned in London on the even of the start of Wimbledon on Monday.
Nadal was joined by David Ferrer and 42 other current and former players and technical staff put their name on the letter which asks the "competent authorities" take swift action to remedy the situation.
They also hit out at "the chaotic and belligerent leadership of Escanuela, which has led to his suspension, putting his personal interests ahead of the sport and deteriorating the image of tennis with his actions."
Fernando Verdasco, Feliciano Lopez and Nicolas Almargo were among the other top players who signed the letter.
Escanuela has refused to give Spain's sports council (CSD) access to financial documents giving the details of the expenses which have been charged to the Spanish Tennis Federation over the last few years.
He and the sports council have also clashed over the federation's appointment in September of Gala Leon as Spain's first female Davis Cup captain, a decision that drew sharp criticism from the nation's top players like Nadal and Lopez.
Leon, who had a career-high ranking of 27 as a player, was a surprise choice to replace Carlos Moya, who stood down after the five-times Davis Cup winners were relegated from the World Group following defeat against Brazil in a playoff.
Toni Nadal, uncle and coach to 14-times grand slam champion Rafa, said at the time that it was "preferable that (the Davis Cup captain) is someone with a background in the world of men's tennis".
Leon presented her resignation last week, but it was not accepted by the tennis federation, Spanish media reported.