In an interview with Rolling Stone, the 'Rocket Man' singer claimed that Joel has yet to take his sobriety seriously.
"He's going to hate me for this, but every time he goes to rehab they've been light," he said. "When I went to rehab, I had to clean the floors. He goes to rehab where they have TVs."
In 2002, Joel sought treatment for alcohol-related issues at a New Canaan, CT rehabilitation facility.
John further asserted that the 'Piano Man' musician will live a happier life if he begins to make his recovery from addiction a priority.
"I love you, Billy, and this is tough love. Billy, you have your demons and you're not going to get rid of them at rehab-light," he added.
"You've got to be serious. People adore you, they love you and respect you. You should be able to do something better than what you're doing now."
Joel has not yet commented on John's comments.
The two Rock and Roll Hall of Fame inductees have teamed for a series of 'Face To Face' world tours over the last 16 years.