The Queen of Soul handpicked Hudson to portray her in the long-gestating movie before her 2018 death, but Kecalf Franklin claims filmmakers have not reached out to her loved ones for their input ahead of its October release.
Taking to Facebook over the weekend (January 04-05), he fumed, "How can you make a movie about a person and not talk to the persons sons or grandchildren about important information (sic)?"
Kecalf went on to insist his mum had only given her blessing to the casting of Hudson. "Everything else is being done against our wishes," he shared.
The biopic is not the only Aretha project Kecalf has taken issue with - he is also angry at photojournalist Linda Solomon for not clearing the release of her forthcoming book, "The Queen Next Door", with her relatives first.
"How can you put a persons family (image) in a book and not ask permission (sic)?" he continued, before appealing to the "A Natural Woman" singer's devotees not to purchase the tome.
"If you are a 'real' fan of my mothers (sic)....please do not support this. Ask yourself....would you want this done to you?"
However, it appears Kecalf's views aren't necessarily shared by his siblings, according to Aretha's longtime attorney, David Bennett, who is also serving as lead counsel for her estate.
"He does not speak for the family," Bennett told the Detroit Free Press. "I know he doesn't speak for his brother Ted White or his brother Clarence Franklin. The grandchildren have absolutely nothing to do with this. What he's really doing is talking for himself."
Kecalf's outburst has also irked movie bosses at MGM, who have been in touch with Bennett about his social media rant.
"They're not happy about it," he said.