The revelation came to light during a federal parliamentary joint committee hearing into the activities of the corporate regulator chaired by Labor senator Deborah O'Neill.
Senator O'Neill told the hearing in Canberra on Friday that she had come across the National Australia Bank's Whistleblower Protection Policy of April this year.
The policy refers potential whistleblowers to KPMG's Fair Call Service, which is described as an "independently monitored external hotline and reporting services".
The evidence came as KPMG, one of the Big Four accounting firms, on Friday revealed its Australian head Andrew Yates had resigned along with audit head Julian McPherson.
They took the fall over the treatment of and the mishandling of allegations by a whistleblower, after an internal investigation into the claims of misconduct was found to have fallen short of the firm's expectations.
"I have been committed to a speak-up culture in our firm, it is clear that in this case we have let ourselves down and I take accountability," Mr Yates said in a statement.
The ongoing internal probe also revealed a separate incident in which documents containing client information were inappropriately shared internally.
There were also allegations of an inappropriate remark in a team setting about the sharing of client information.
Asked if the corporate regulator would investigate, Australian Securities and Investments Commission deputy chair Sarah Court said it would make inquiries.
"We are very interested," she told the joint committee on corporations and financial services.
Senator O'Neill said she was aware NAB wasn't the only corporation using the KPMG service.
"Some of the most significant firms in this country seem to be using this service, which gives me pause," she told the hearing.
"Who triaged the Fair Call KPMG whistleblower services? What companies were involved?
"I can say a little bit of digging so far has revealed that the RBA (Reserve Bank of Australia) and the ASX (Australian Securities Exchange) actually avail themselves of this whistleblower service, which just blows my mind."
ASIC on Friday also confirmed it had begun a preliminary investigation into the conduct of at least three KPMG registered company auditors.
The probe is happening amid allegations that auditors working on a Lendlease matter retained and utilised access to audit tender pictures from the building company's board papers to "inform" their tender for Westpac's audit business.
Commissioner Kate O'Rourke stressed the investigation related to the auditors rather than the firm.
"We commenced these inquiries after a meeting with KPMG on the 14th of April, and then after receiving further anonymised, in that case, information in writing from KPMG, on the 29th of April," she added.
Regarding KPMG's own investigation, Ms Court said the regulator had issued a number of notices to KPMG for the production of information.
