New York-based Gary Zimet posted the missive - in which Salinger discusses plans for a movie version of his classic novel The Catcher in the Rye - on his website more than a year ago.
But he has now received a notice from officials at Salinger's trust demanding the removal of the letter, according to New York Post gossip column PageSix.
In the note, Salinger discusses his thoughts on any potential big-screen version of his famed 1951 book, writing, "Since there's an ever-looming possibility that I won't die rich, I toy very seriously with leaving the unsold rights to my wife and daughter as a kind of insurance policy. It pleasures me no end though, I might quickly add, to know that I won't have to see the results of the transaction."
In a letter obtained by PageSix editors, the author's son Matt Salinger writes, "Any publication - even online - without express permission by my father and/or the Trust is a direct and clear infringement of my father's, and now the Trust's, intellectual property rights... We have referred this matter to our attorneys."
Salinger died at the age of 91 in January, 2010, of natural causes.