Labor is seeking to have Liberal MP Tim Wilson referred to the parliament's powerful privileges committee over issues relating to an inquiry he chairs.
Mr Wilson is chairing an inquiry into Labor's franking credits policy.
But Labor frontbencher Tony Burke told parliament on Wednesday there is evidence Mr Wilson may have "improperly interfered in the free exercise of the committee's functions".
Mr Burke says this would amount to Mr Wilson being in contempt of the House of Representatives.
The Liberal MP has acknowledged his official website, which encouraged people to give evidence to the inquiry, also included a petition from Wilson Asset Management.
He holds shares with the fund manager and is a distant cousin of its owner.
But he failed to declare this conflict of interest to the committee and even at public hearings when that relative - Geoff Wilson - spoke at a public hearing in November last year, Mr Burke said.
"At one point during the hearing, Mr Geoff Wilson spoke about his shareholders. But the chair, even then, failed to declare his obvious conflict of interest," Mr Burke added.
This also breaches parliamentary rules which prevent MPs from being on committees where they have a pecuniary interest in the matter under inquiry, the Labor MP said.
"The committee will be forced to rely on evidence which has been prejudiced by actions of the chair."
Mr Wilson shook his head and took notes as Mr Burke spoke, at times laughing to himself and even yelling out "rubbish" to Labor's claims.
The parliamentary inquiry is unusual in that it is investigating an opposition policy and has not scheduled formal witnesses, having instead opted to give members of the public three minutes each to speak at "town hall" style meetings.
Labor also raised issues with Mr Wilson's website, particularly a now-fixed requirement for people to sign a petition against Labor's policy in order to register for a hearing.
The website collects private information about people, but "it is not clear who has access, or who will have access to this information," he said.
Mr Burke also singled out Liberal MP Jason Falinski for encouraging hearing attendees to attend a Liberal Party fundraiser, as well as his colleague Andrew Wallace for calling on people to join the party as he gave evidence.
Labor has contacted the committee of privileges and members' interests after the Liberal MP only updated his register of interests on Wednesday to disclose he is a director and shareholder of Bolger-Wilsons Investments Pty Ltd.
Speaker Tony Smith will consider the issues and report back the house on his findings.
The opposition has also referred Mr Wilson to the Australian Federal Police over claims personal data gathered by the parliamentary inquiry was given to a fund manager.
