Attorney-General George Brandis has stamped out suggestions potential changes to marriage laws could pave the way for polygamous unions.
One Nation leader Pauline Hanson pressed Senator Brandis in parliament on Monday about the possibility future parliaments may amend marriage laws to appease minority groups.
"The question will be to allow same-sex couples to marry. The question is specifically in relation to couples. Two people. Not more. Two people," Senator Brandis said of an upcoming postal ballot on same-sex marriage.
"I can give you my absolute assurance that, in the event that if the plebiscite question were to be resolved 'yes', the bill that will come to the parliament will deal with couples, will deal with marriage between two people."