Former PM Tony Abbott is advocating a 'no' vote in the same-sex marriage postal plebiscite.
Malcolm Turnbull has won rare praise from Tony Abbott over the prime minister's decision to hold a postal ballot on same-sex marriage.
"Well done to Malcolm Turnbull and the government for making sure this is going to happen," the former prime minister told reporters in Canberra before outlining his argument for a 'no' vote.
"If you don't like same-sex marriage vote 'no', if you're worried about religious freedom and freedom of speech vote 'no', if you don't like political correctness vote 'no'."
Voting 'no' would "stop political correctness in its tracks".
Mr Abbott vowed to respect the majority view of Australians.
"And I call on both sides of this debate to respect whatever result the plebiscite gives us," he said.
Whether Australians vote in a compulsory-attendance plebiscite on November 25 or take part in a voluntary postal ballot from mid-September is likely to be decided in the Senate this week.
The government is recommitting its rejected plebiscite bill to the upper house on Wednesday.
Another former Liberal prime minister is also backing the government's decision.
John Howard says the government had no alternative but to keep faith with its election promise.
"I think the prime minister has done exactly the right thing in proposing what it's proposing and let us see what the Senate does," he told reporters in Canberra.
Mr Howard was responsible for amending the Marriage Act in 2004, with the support of Labor, that limited the definition of marriage to between a man and a woman.
Deputy Labor leader Tanya Plibersek insists the best possible option is a free vote in parliament this week or next.
"John Howard took an afternoon to change the Marriage Act," she told ABC radio.
Ms Plibersek would not say whether Labor would campaign for a 'yes' vote if a postal ballot went ahead.
Liberal backbencher Andrew Laming is comfortable with the $170 million price tag for the plebiscite or $122 million cost of the postal ballot.
"The cost of democracy is not insignificant. I can take you to a country where you won't have to worry about $150 million price tag - North Korea," he told reporters.
The MP wants an advertising blackout and no foreign campaign donations.