Asked about the shareholding on Tuesday, Mr Wilson promised to publicly disclose it at the start of future hearings.
The franking credits inquiry is unusual in that parliamentary committees do not usually investigate opposition policies. About $160,000 in public funding is being spent on venues, accommodation and travel.
It can also be revealed Mr Wilson and Geoff Wilson are related: the MP’s great grandfather is the fund manager’s grandfather.
Labor has now called on Mr Wilson to resign as chair of the inquiry due to «scandalous and highly unethical» conduct. The brawl threatens to dint the Morrison government’s criticism of Labor’s proposed changes, which could see self-funded retirees lose up to $5 billion a year in refunds.
Mr Wilson’s parliamentary committee has travelled around Australia hearing evidence from hundreds of people concerned about what the policy could mean for their retirement incomes.
Audio of an investor-only phone call in September reveals Geoff Wilson boasted of discussions with Mr Wilson months before the public hearings began.
«We have to maintain the pressure so we get the result,» the fund manager told investors.
«I was saying it would be nice if one of the hearings could be on a day we are doing a roadshow. Then we could do a little protest, we could have our placards and we could walk down there.»
Wilson Asset Management’s «franking credit roadshow» coincided with a hearing of the parliamentary inquiry in Sydney on November 20.
«I met with a range of stakeholder groups in the lead up to the first round of hearings to promote attendance, and actively encouraged participation, including from Geoff Wilson,» Mr Wilson said in a statement.
«Many groups across Australia have been outraged by Labor’s retirees tax grab and they wanted their voices heard.»
Under an entry listed as a «shareholding», Mr Wilson’s register of parliamentary interests shows he and husband Ryan Bolger invested in a Wilson Asset-managed fund in May 2017 through the couple’s self-managed superannuation fund.
They invested in another Wilson Asset fund, WAM leaders, in December 2017.
Labor MP Matt Thistlethwaite said Mr Wilson should resign as chairman.
«Not only did he create a blatantly partisan website but it now appears he has an interest in a company that is leading the charge against Labor policies,» he said.
«That is highly unethical and it taints the inquiry.»
Labor’s shadow treasurer, Chris Bowen, also called on Mr Wilson to resign.
«The case is clear and overwhelming. It’s time for Tim Wilson to resign,» Mr Bowen said on Wednesday morning.
Geoff Wilson has told the inquiry some of his clients could lose up to $30,000 a year through Labor’s policy to strip tax refunds from retired shareholders who have not paid tax.
In a statement, Geoff Wilson said: “We have fought this policy on behalf of our 80,000 shareholders since it was announced on 27 March 2018. Modest retirees and low-income earners will be devastated by this policy and we have worked to give them a voice.»
The committee has no formal witnesses scheduled for the 12 town hall-style meetings. At one recent hearing, a government backbencher handed out Liberal Party membership forms.
The inquiry is also accompanied by the Stop the Retirement Tax website. The «Stop the Retirement Tax» slogan was first coined by Wilson Asset Management on September 20 when it launched its own online petition.
Five days later, Geoff Wilson told investors he had spoken to Mr Wilson about coordinating hearing dates. Within a month, the government’s official «Stop the Retirement Tax» website was established.
The government site and Wilson Asset Management sites use identical photos.
Mr Wilson said he was responsible for the content on the website and Geoff Wilson «was just one of many stakeholders consulted with its development to maximise its efficacy and ensure it had impact to encourage participation».
Until Sunday, the website appeared to prohibit those who did not want to sign a petition from attending the public meetings with MPs.
Geoff Wilson wrote an opinion piece for The Sydney Morning Herald and The Age on Tuesday arguing Labor would come to regret labelling the refunds as welfare for the wealthy.
Eryk Bagshaw is an economics correspondent for The Sydney Morning Herald and The Age.