Labor's demanding an investigation of a trip Human Services Minister Stuart Robert took in August 2014 during which Liberal Party donor Paul Marks finalised a mining deal.
Parliamentary records show Mr Robert, who was then assistant minister for defence materiel, is a shareholder in Mr Marks's companies.
But Mr Robert insists he attended in a private capacity and paid for the trip himself.
Labor Senator Stephen Conroy says a full investigation needs to be conducted.
"And ultimately if all of the facts are that Stuart Robert has used his position as a minister to promote a company that has made major donations to the liberal party, that he is a personal investor in then he has to go."
Federal Treasurer Scott Morrison dismissed claims of ministerial misconduct, saying the whole issue is a "shocking beat up".
