The letter comes after Miley's Rolling Stone interview, in which she said her video for 'Wrecking Ball' was designed to be similar to Sinead's 'Nothing Compares 2U'.
'The music business doesn’t give a s**t about you, or any of us,' the singer continued. 'They will prostitute you for all you are worth, and cleverly make you think it's what YOU wanted… You are worth more than your body or your sexual appeal.'
Wise and empowering words, but O'Connor isn't the only star weighing in on Miley's controversial behaviour.
Click on to see what the rest of celebdom had to say…