The stoner icon, who endorsed the Democrat for U.S. President earlier this year (16), claims he was asked to introduce the Senator at the event and then told he was no longer needed hours before.
The outspoken marijuana advocate tells The Hollywood Reporter someone got "cold feet" at the idea of Sanders appearing onstage with him.
"It's lip service to get the votes," he says, "but they don't want to endorse what I stand for and what I've stood for all my professional career. It was an insult."
A Sanders spokesman tells the publication, "We appreciate his support but a scheduling issue came up."