Big four consulting firms are set to face a new inquiry over PwC tax leaks. 

A recent tax scandal involving PwC has led to a new Senate investigation into conflicts of interest at Australia's four major consulting firms. 

The inquiry will focus on unethical behaviour by consultants hired for lucrative federal government work. The inquiry will run until September 26, 2023, and will be conducted by the Finance and Public Administration Committee.

The investigation follows the deregistration of PwC's former head of international tax, Peter Collins, by the Tax Practitioners Board for dishonesty and for sharing confidential government briefings with PwC partners and clients. 

PwC was also sanctioned for failing to regulate conflicts of interest by partners and staff who knew the confidential information would be used to help clients sidestep new tax laws and to attract new clients.

Greens senator Barbara Pocock pushed for the inquiry that was approved by the Senate on Thursday. The One Nation party supported the inquiry. 

Senator Pocock says taxpayers deserve to know whether major firms provide value for money in their lucrative contracts with the government. 

She also stressed that recent examples highlight serious problems with transparency, integrity, and outcomes.

The inquiry will also examine growing concerns around the use of consultants by the federal government, including the high cost of external advisers, frequent cost overruns, and the de-skilling of the public service. 

The government is already exploring ways to cut its $2 billion annual consulting bill and increase the skills and capability of the public service, including the possibility of creating an in-house consulting service.

PwC's CEO, Tom Seymour, has denied that up to 30 partners and staff were involved in the sharing of confidential information, contradicting evidence heard by a Senate committee last month. 

Instead, he describes the firm as having a “perception issue” for not having an effective system in place at the time to manage confidentiality agreements signed by its advisers.