Malcolm Turnbull will ask the head his department to investigate claims former Liberal minister Bruce Billson breached ministerial standards.
It has been reported Mr Billson lobbied MPs while working for the Franchise Council of Australia barely six months after losing the small business portfolio.
"I will raise it with the secretary of my department to investigate," the prime minister told parliament on Thursday in response to a question from Labor.
The ministerial standards ban former ministers from lobbying members of parliament on any matter relevant to their previous portfolio within 18 months of leaving the job.
