The late star is said to have barred siblings from his Neverland ranch if the pet did not like them.
Michael reportedly told staff: ''He is a good judge of character.''
A former housekeeper told The Sun newspaper: ''Bubbles often would be a gauge for Michael to decide who should stay and go.''
The revelation comes around the time that the performer's family endure an argument over his millions, three years after his death in Los Angeles aged 51.
His ex-employee said Michael would react to Bubbles response to his various relatives.
He would say: ''They are only after my money.''
Brothers Jermaine and Randy were said to be among those regularly snubbed.
Jermaine recently defected from a family letter criticising the Michael Jackson Estate.
However he still has ''deep reservations'' about the executors.
Jermaine posted a long letter on his twitter account confirming the move.
He wrote: ''I rescind my signature from the letter which was sent to the Estate, and which should never have gone public.''
''I still hold deep reservations about many issues involving the Estate, and I will continue to bring scrutiny and a resolute voice wherever we have cause for concern. But the way to address such matters is through the proper channels and via a private dialogue, not public conflict.''
''In this spirit, I offer this statement by way of extending an olive-branch.''