Former prime minister Tony Abbott has kicked off his campaign for a 'no' vote in a postal plebiscite, urging Australians to reject same-sex marriage if they want to protect religious freedom and reject political correctness.

"Obviously I will be voting no. But in the end this is not about the politicians, this is about the people, it's about your view," he said on Wednesday morning.

"And I say to you if you don't like same-sex marriage, vote no. If you're worried about religious freedom and freedom of speech, vote no, and if you don't like political correctness, vote no because voting no will help to stop political correctness in its tracks."

The Turnbull government on Tuesday agreed to hold a $122 million non-compulsory, non-binding plebiscite on whether same-sex couples should be allowed to marry. Ballots will likely be posted from September, should the plan survive a likely High Court challenge.