Two senior Government frontbenchers have refused to say whether they would back same-sex marriage in Parliament if a plebiscite on the issue was carried.

The Coalition has promised to hold the public vote on the issue if it wins power, however, the result is non-binding and still needs to be passed through Parliament.

Coalition MPs have been told they will be given a free vote in Parliament, regardless of the result of the plebiscite.

In separate interviews, Treasurer Scott Morrison and Foreign Minister Julie Bishop avoided questions on how they would vote.

In an interview on 7.30, which also focused on the Coalition's costings ahead of the election, Mr Morrison was repeatedly asked how he would vote on if his own electorate supported changing the Marriage Act.

But Mr Morrison, who regularly speaks publicly about his Christian faith, would not be drawn in the interview with Leigh Sales.

Sales: Why can't you answer it clearly — will you vote for same-sex marriage? Mr Morrison: I will use my words, you use yours and you're not allowed to put words in my mouth. Sales: I think if that answer doesn't make it clear, I want clarity for my audience; will you vote for same-sex marriage? Mr Morrison: I will respect the outcome of the plebiscite. If it passes then the legislation will pass. Sales: With your vote? Mr Morrison: I will respect the outcome of the plebiscite. Sales: I'm not sure why you can't answer if it will be with your vote. Mr Morrison: I get to choose the words I use as a politician, you get to use the words you use to put questions, that's how it works. Sales: We will allow our viewers to make their judgement as to what they think you will do.

In an interview on Lateline, Ms Bishop was asked how she would vote in Parliament, if the majority of Australians supported marriage equality in the plebiscite but her electorate voted against it.

But Ms Bishop would not be drawn, saying she would wait until she saw the legislation.

Emma Alberici: If the plebiscite does go ahead and the majority of Australians support marriage equality, but your specific electorate votes against same-sex marriage, how will you vote in the Parliament? Ms Bishop: Well, that will depend on the plebiscite vote overall, how it is broken down and what it looks like, state by state, electorate by electorate and then, of course, it will depend what the legislation looks like. But I would respect the outcome of the plebiscite obviously. Alberici: But would you be more inclined to vote on how the majority of Australians have voted or how your particular electorate voted? Ms Bishop: Well, I would take my electorate's views into account, but I would also take into account how the plebiscite played out across Australia because, for example, a referendum gets up if it is the majority of states, majority of people in the majority of states. So if that is the way it played out — Alberici: Pardon the interruption, though. This is not a referendum? Ms Bishop: I know that. I was saying if it were a referendum, people usually see a majority vote in a majority of states. As a plebiscite, if majority passes it across Australia, that is pretty compelling. Alberici: And that is how you would vote? Ms Bishop: I would wait until I see the legislation. This is all hypothetical. What we have said is we will have a plebiscite so everybody in Australia can have their say and I support that and I think it is a good idea. Alberici: But you won't tell us how you would eventually vote, whether you would follow the mandate of the people if they have decided to vote as a majority in favour of marriage equality? Ms Bishop: Well, I always have a look at what the legislation says and I will respect the outcome of the plebiscite.

The Opposition has promised to introduce same-sex marriage legislation into Parliament in the first 100 days of a Labor government.

Mr Morrison drew controversy last week when he weighed in on a speech by Labor's openly gay frontbencher Penny Wong, who feared the marriage equality plebiscite could stoke hatred and homophobia.

Mr Morrison said people of strong religious views had also endured hatred and bigotry, as well as members of the LGBT community.

Those comments were dismissed by Opposition Leader Bill Shorten.

"I do accept that people of faith do get a hard time sometimes ... and people of religious faith are entitled to respect," he said.

"But what I don't understand is why the Treasurer of Australia feels the need to drive across two paddocks, cross three rivers and get to a bridge, to talk about Penny Wong's remarkable speech."