As a rule, I don't provide a client's info to any third party.  I give them their copy (hard, or PDF) then they can share as they see fit.  Eliminates a ton of possible liability.

IF you choose to send your client's info to a third party, ye - there's an authorization form.  I use the one recommended by either the AICPA or my E&O insurance carrier.

thank you

YVW

ps - do you know the form name or number?  i am on the aicpa website and cannot locate it