In a second legal notice in three days, Tata Sons alleged that Mistry had "wrongfully and dishonestly" taken confidential information out of the company premises without consent.
It asked him to "immediately return to the company all confidential information" in his possession and "not retain copies" of the same.
Asking him to cease from use or disclosure of confidential information, the holding company of the USD 103-billion salt-to-software group also asked Mistry to sign an undertaking within 48 hours that he "shall preserve the confidentiality of all the confidential information and not use or disclose" to anyone, including affiliates, relatives and family members.
On Tuesday, it had sent a legal notice accusing Mistry of breaching confidentiality rules by attaching dozens of confidential and sensitive company documents with the petition filed by his family investment firms before the National Company Law Tribunal against his removal.
It had threatened to take legal action against him, terming his action as "reckless failure" in discharging of "fiduciary, legal and contractual duties".
In today's notice served through its law firm, Tata Sons said Mistry was privy to confidential and commercially sensitive information and documents in his capacity as executive chairman and director of the company and its operating firms.
"Under applicable low, you are duty-bound to (a) preserve the confidentiality of all such information and data that you are privy to in your capacity as director and (b) not disclose or use such information for any purpose whatsoever," it said adding any breach of such legal duties would cause irreparable harm and injury to Tata Sons.
Mistry, it said, is in "possession of highly valuable information and documents" pertaining to Tata Sons and Tata Group companies, which he has "disclosed" without prior authorisation from the board.
"We have credible information that you have wrongfully and dishonestly taken movable property being Confidential Information, out of the possession of the company, from the premises of the company, without taking the appropriate consent of the company," the notice said adding such an act was an offence punishable by law.
It asked him to "immediately return to the company all confidential information" in his possession and "not retain any copies" as well as "cease any and all use or disclosure of Confidential Information".
Also, Tata Sons wanted Mistry to execute an undertaking stating that he has returned all the confidential information without retaining any copies.
The undertaking also wants Mistry to state that he will "preserve the confidentiality of all Confidential Information and not use or disclose such Confidential Information for any purpose whatsoever and shall not provide any such Confidential Information to any affiliates, relatives and family members".