Sony Music has dismissed claims that vocals on a new Michael Jackson album are not those of the star.
It said at the weekend it had "complete confidence" they were genuine after TMZ.com reported that his two eldest children thought otherwise.
On Monday, new track Breaking News, from the forthcoming album, Michael, was posted on the singer's website.
His nephews, TJ and Taryll Jackson, have now complained on Twitter about the track's "fake" and "shady" vocals.
Sony said in its statement that it had "complete confidence in the results of our extensive research, as well as the accounts of those who were in the studio with Michael, that the vocals on the new album are his own".
A brief excerpt from Breaking News was featured on Jackson's website on Friday before the full song was posted on Monday.
It begins with a montage of news clips reporting on controversies surrounding the singer and features the lyrics: "Everybody wanting a piece of Michael Jackson, reporters stalking the moves of Michael Jackson, just when you thought he was done, he comes to give again."
TJ Jackson, son of the singer's brother, Tito, wrote on Twitter: "Deceptively merging shady vocals with MJ samples - from prior MJ records - will never fool me."
He said he had heard the vocals on their own and they contained "sampled breaths after sampled breaths mixed in with fake vocals to try to fool you".
Taryll Jackson, also Tito's son, said there were "songs that are my uncle singing on the upcoming album and I will support those 100%".
"But I will not support Breaking News and a few others because it simply is not him."
Michael, which is due for release in the UK on 13 December and in the US a day later, contains tracks he had been working on before his death in June 2009 and which have been completed posthumously.
In August, Black Eyed Peas frontman Will.i.am, who had been working with Jackson, said the album should not be released.
"He was a perfectionist and he wouldn't have wanted it that way," he said.
"Now that he is not part of the process, what are they doing? Why would you put a record out like that?"
Meanwhile, an interview between Oprah Winfrey and Jackson's mother, Katherine, will be shown in the US on Monday.
The interview, at the Jackson family home, near Los Angeles, will also feature the singer's children, Prince Michael, 13, Paris, 12, and Prince Michael II, eight, also known as Blanket.