Treasurer won't hold back on gay marriage

Treasurer Scott Morrison says he will actively campaign against same-sex marriage when it comes to a national vote.

The coalition has pledged to hold a plebiscite on changing marriage laws if re-elected later this year, but Mr Morrison is among senior government members who oppose any change.

"I don't plan to keep my opinion to myself on these issues and I don't think anyone should - that's the whole point of having a plebiscite," he told 2GB radio on Monday.