Labor has referred Liberal MP Tim Wilson to the Australian Federal Police over claims personal data from a government inquiry was given to a fund manager.
Labor MP Matt Thistlethwaite has written to the AFP to investigate whether Wilson, who is chair of the inquiry into Labor's franking credit policy, had shared with Wilson Asset Management the details of voters who had signed up to give evidence.
It comes after reports that people who had registered with the MP's website were receiving advertising from the fund - which is owned by his distant relative, Geoff Wilson.
In a statement on Friday Mr Wilson said he "personally contributed" to funding the 'stop the retirement tax' website, but insisted he had only communicated with shareholders and signatories of the petition.
Shadow assistant treasurer Andrew Leigh said Labor would "certainly be pursuing this issue" when parliament returned next week.
"Australians don't want parliamentary inquiries that then see their confidential elector data, protected by law ... then shared with private firms," he told the ABC.
Prime minister Scott Morrison defended Mr Wilson to reporters on Saturday and said he would not be removing him as chair of the inquiry.
"I think Tim is giving a voice to retirees all around the country and the Labor party can't stand it."
The prime minister said he was "not surprised" Labor is "furious" about the public hearings being held into their proposal to end the practice of cash refunds for "excess" franking credits.
The practice involves giving a tax credit to shareholder dividends to offset any company tax already paid on the profit - ensuring there isn't a double tax.