Securities and Exchange Board of India (SEBI) has begun a preliminary review of the resignation letter of former HDFC Bank chairman Atanu Chakraborty for possible violations of rules governing directors of listed companies, two sources familiar with the matter said.

Chakraborty told Reuters he was not aware of any examination by the regulator.

In his resignation letter, Chakraborty cited "certain happenings and practices within the bank" that he said were "not in congruence" with his personal values and ethics.

He did not elaborate. The letter triggered an 8.7 per cent slide in the stock the following day and wiped $16.3 billion in market value over three sessions.

Regulator making checks

A department of SEBI that oversees corporate disclosures and governance is examining the former chairman and other directors for alleged failures to do their fiduciary duties, the sources said.

"(The) examination is to verify claims made in the resignation letter and whether other directors were aware of any material information and did not document them," one said.

The Reserve Bank of India, the primary regulator in the case, said last week it had found "no material ​concerns on record as regards its (bank's) conduct or governance".

"We are also checking if there was any misreporting of any events which could impact minority investors," the first source said, adding that SEBI was reviewing the adequacy of disclosures by both the bank and Chakraborty.

India's rules for listed companies require independent directors to assess the quality and timeliness of information flow between management and the board.

Email queries sent to HDFC Bank and SEBI were not immediately answered.

Chakraborty told Reuters by text that he had not made any insinuations in his letter. He added that no one from the regulator had contacted him and that he was unaware of any SEBI review.

Earlier this week, SEBI Chairman Tuhin Kanta Pandey, without commenting on individual cases, said independent directors must follow the code of conduct set ​out in regulations.

"No one can make insinuations without proper evidence being recorded," Pandey said. "Any such comments do have an impact on minority shareholders .... Independent directors have to be responsible in ⁠terms of ​what they say."

HDFC Bank said on Tuesday it had appointed external law firms to independently assess the concerns raised in the resignation letter. Chakraborty told Reuters the firms had not contacted him.