MPs will take gay vote seriously: Truss

Coalition MPs will take the outcome of a plebiscite on gay marriage very seriously, Deputy Prime Minister Warren Truss says.

The Nationals leader says MPs have a right to vote as they see fit, after conservatives Eric Abetz and Cory Bernardi insisted coalition MPs would not be bound if Australians voted in favour of marriage equality.

"In reality, when people have spoken by way of a referendum, that will be a very powerful argument, I think, in the minds of members of parliament," he told reporters in Adelaide.

Mr Truss would not say whether he expected Nationals MPs to respect the outcome of the plebiscite.

"Every member of parliament, particularly on the coalition side, has a right to a conscience vote and a right to dissent if they feel so inclined," he said.

"But clearly when the people have spoken, that is a very powerful argument that I'm sure every member would take into account."