The Greens senator Barbara Pocock has warned consultancy PwC Australia faces fresh scrutiny after the Australian Taxation Office revealed it had queried advice given to clients that might “mislead or subvert” foreign investment review board processes.

The details were revealed in answers to questions Pocock put to the ATO about a meeting between the office commissioner Jeremy Hirschhorn and the then PwC chief executive, Luke Sayers, in August 2019.

At that meeting, Hirschhorn “advised” Sayers about concerns with PwC’s tax practice. These had followed a 2015 tax scandal that prompted regulators to bar PwC’s Peter Collins from advising for eight years after he was accused of sharing confidential government information about multinational tax avoidance with his colleagues.

Among the issues raised was a concern about PwC’s “involvement in Foreign Investment Review Board approval processes on behalf of clients which, through omission and commission, had the potential to mislead or subvert those processes”, the ATO said.

“These are serious and new allegations and need to be thoroughly investigated,” Pocock told Guardian Australia.

The ATO’s responses come about a week before a Senate inquiry into consultants – led in part by Pocock – is due to release its final report on 12 June after a couple of extensions.

Pocock’s office said a separate inquiry into corporations led by Labor’s Deb O’Neill, might get a chance to investigate the ATO’s concerns more closely.

Guardian Australia sought comment from PwC and the treasurer, Jim Chalmers, who oversees the foreign investment review board.

In its response to Pocock, the ATO also said it had raised concerns with PwC about it “assisting clients in the preparation of responses to Request for Information (RFI) notices for clients, where material in those responses was false or misleading to the knowledge of the PwC staff involved”.

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The ATO also said that “Hirschhorn read out several representative PwC emails to Mr Sayers which had been previously provided to the ATO by PwC”.

Pocock raised the issue about the emails in her questions to the Australian Investments and Securities Commission in Senate estimates on Tuesday.

Noting Sayers was paid $30m over eight years, Pocock asked the Asic chair, Joe Longo: “Mr Luke Sayers’ constant response throughout this series of events is ‘I have no memory.’ How plausible do you think that position is?”

“I’m not in a position to comment one way or the other as to who’s telling the truth,” Longo told Senate estimates. “But certainly, from my perspective on the face of it, it’s a very serious situation.”