The Commerce Commission is to investigate whether its deputy chairman, Donal Curtin, provided an appropriate level of disclosure of interests.
Mr Curtin was appointed deputy chair of the commission in July.
Hugh Rennie QC will investigate whether Mr Curtin provided appropriate disclosure to the commission and the Commerce Minister in relation to his involvement with three finance and investment companies.
The commission says disclosure of conflicts of interest by members of crown entities is required under the Crown Entities Act 2004, and commission members are required to provide full disclosure of any potential interests under the organisation's policy on conflicts of interest.
Mr Curtin has voluntarily stood down during the inquiry.