Mistry, who still remains a Director on the board of the holding arm of the the $100 billion-plus group, was asked to desist from such alleged actions.
Mistry was served the notice after the holding company of the industrial conglomerate Tata Group filed a petition before the National Company Law Tribunal (NCLT) Mumbai for alleged 'breach of confidentiality obligation by a Director'.
The notice was served to Mistry by leading law firm Shardul Amarchand Mangaldas.
According to the notice, Mistry passed on sensitive information which he was privy to under the capacity of a Director of Tata Sons to companies owned and controlled by his family.
Mistry's family controlled companies -- Cyrus Investment Private Limited and Sterling Investment Private Limited -- are petitioners against Tata Sons before the NCLT (Mumbai).
"By passing on confidential and sensitive information accessed by you in your capacity as a Director of Tata Sons to companies owned and controlled by your family, that is, the petitioners, you have acted in complete violation of your confidentiality undertakings to Tata Sons, your fiduciary duties towards Tata Sons and your obligations under the Tata Code of Conduct," the legal notice said.
"We demand that you cease and desist from sharing any confidential and sensitive information accessed by you in your capacity as a director of Tata Sons with the petitioners," the notice said.
It added: "We also demand that you ensure that any such information which is sought to be used in legal proceedings, any documents or parts thereof which are unrelated to the matters being agitated in such legal proceedings are suitably redacted."
The Tata Sons legal notice accused Mistry of acting recklessly with the sole intent to "cause harm and loss" to its clients.
"Clearly, you have been entrusted with confidential and sensitive information, which is in the nature of property, in your capacity as director, and you have deliberately used such confidential and sensitive information in violation of law to cause wrongful loss to our client and the Tata Group Companies," the notice said.
"Thereby, your actions and omissions have resulted in a criminal breach of trust," it added.
"Such reckless failure on your part in discharging your fiduciary, legal and contractual duties has caused irreparable harm and damage to Tata Sons and the Tata Group and our client intends to exercise all legal rights and pursue all remedies available under applicable law to our client in relation to such breach on your part," the notice said.
It said Mistry's actions and omissions has exposed Tata Sons to potential claims from third parties for breach of confidentiality and "our client has every intention to make you liable for all such claims."
"Our client strongly believes that your actions and omissions by itself is an act of mismanagement. Such deliberate acts and omissions on your part, clearly establishes the fact that contrary to all your claims, you are no well-wisher of Tata Sons and the Tata Group Companies."