Michael Jackson's estate is calling BS on an upcoming auction of a "Thriller" jacket ... claiming the auction isn't making it clear MJ never actually wore it in the iconic music video.

In a letter fired off Tuesday to Gotta Have Rock and Roll, the auction house, the estate's attorney, Jonathan Steinsapir, declares -- in no uncertain terms -- the jacket up for sale wasn't on Michael's back at any point during production of the "Thriller" short film.

Jonathan writes there were only 2 genuine "Thriller" jackets worn in the film, and one was auctioned for nearly $2M over a decade ago -- which is 20 times more than the minimum bid GHRR is seeking for their jacket.

The Jackson Estate also has serious concerns about GHRR's listing, because it could mislead the public into believing the real deal "Thriller" jacket has lost considerable value -- and that could negatively impact MJ's brand and the value of other personal items.

While the estate acknowledges GHRR clarified in the auction description that the jacket "was not worn during the 'Thriller' music video" ... it's demanding the auction house make this fact more visible in the title of the auction, and clarify they have no proof Michael ever wore this particular jacket for promotional purposes.

And, it looks as though GHRR has fallen in line.

Since the letter was sent, the auction has changed its title to include the word "style" ... and now reads, "Michael Jackson 1983 Owned & Worn Thriller Style Jacket."