Michael Douglas and Ex-Wife Told, Sorry, Your Son's No One Special

Michael Douglas and his ex-wife, Diandra have just been derailed in their effort to see their imprisoned son -- ironically derailed by a group that fights for prison reform ... TMZ has learned.

Cameron Douglas is currently serving time on drug charges and prison officials are not letting visitors see him -- including his parents.

Diandra has been enlisting Hollywood celebs to sign a petition posted on Change.org -- a petition urging prison officials to let them see their son.

Her campaign was picking up steam but suddenly it disappeared from the website with no explanation.

We did some digging, and contacted the Drug Policy Alliance, which actually spearheaded the petition drive. DPA officials told us they had a change of heart ... the sentiment was that it was unfair to help individuals and not focus on the big picture of prison abuses. It seems there was also a feeling that it didn't look good to help famous people and not everyone else.