Former Liberal minister Bruce Billson is weighing up his future as head of a powerful business lobby as he faces two federal investigations into an undisclosed salary the group paid him while he was still an MP.

"I'm currently considering my position as executive chairman of the [Franchise Council of Australia]," Mr Billson said in a statement after the Opposition asked for a parliamentary inquiry into whether the former member for Dunkley acted corruptly so as to be in contempt of parliament.

Last week, 7.30 revealed Mr Billson failed to declare he was receiving a $75,000-a-year salary from the FCA, months before he was due to retire from parliament at the 2016 federal election.

The Abbott government's small business minister has apologised for failing to disclose the salary on the official register of interest, and denied the position generated a conflict of interest.

'These matters raise serious concerns'

Labor has asked Speaker of the House Tony Smith to refer the matter to the Standing Committee of Privileges and Members' Interests to decide whether Mr Billson should be found in contempt of parliament.

"These matters raise serious concerns about the motivation for every action Mr Billson took as a member of parliament while he was reportedly being secretly paid by the Franchise Council of Australia," Manager of Opposition Business Tony Burke said in Parliament yesterday.

Former small business minister Bruce Billson speaking in parliament. ( ABC News: Nicholas Haggarty )

Mr Burke wants the investigation to also examine whether, "the Franchise Council of Australia or any of its staff or directors has, by appointing and paying Mr Billson as a director of that lobby group while he was still a member of the House, sought to bribe or has bribed a member of the House such as to constitute a contempt of the House".

Past and present MPs found guilty of contempt face potential penalties of six months in prison or a $5,000 fine.

Mr Smith told Parliament he would consider the Opposition's request and report back as soon as possible.

Last year, former Labor MP Craig Thomson was found guilty of contempt for misleading parliament in a 2012 speech in the House.

Prime Minster Malcolm Turnbull last week ordered a separate investigation into whether Mr Billson breached standards preventing former ministers from lobbying MPs on matters related to their former portfolio within 18 months of leaving the job.

Mr Billson said he would cooperate fully with any inquiry.