A SENATOR says the Federal Government will waste $100m if it goes ahead with its planned plebiscite on same-sex marriage.

The Senate on Thursday debated a Greens bill redefining marriage as a union between "two people".

The bill also allows for same-sex couples married overseas to have their relationship recognised in Australia.

South Australian Greens senator Robert Simms said the same-sex marriage plebiscite planned for after the next election was a waste of money as most Australians supported gay nuptials.

"Can anyone seriously suggest that we should be spending more than $100 million of taxpayer funds on a question we already know the answer to?" Senator Simms said.

"The last thing I want is to see taxpayer money being spent on a divisive campaign against marriage equality, what in effect would become a state-sanctioned, state-funded hate campaign."

Nationals Senator Matthew Canavan said changing the Marriage Act so it breached religious views of marriage would contravene human rights.

- APN NEWSDESK