Lindsay Lohan -- Dina Lohan Drunk Dialed Therapy Session

Lindsay Lohan's mother has been banned from participating in her rehab treatment after a drunken phone call a few weeks ago ... TMZ has learned.

Sources tell us shortly before Lindsay's birthday, July 2, Cliffside rehab facility got Dina on the phone -- so LiLo could have a conversation with her.

But we're told the person from the clinic who spoke to Dina believed she was hammered, and quickly nixed the idea of letting her speak to Lindsay.

Furthermore, we're told the rehab team felt it would be best for LiLo's treatment if she stopped talking to Dina altogether for the rest of her stay.

Good luck, Oprah.

Attempts to reach Dina were unsuccessful.