Australia's government has all but destroyed legislation that would allow gay marriage by refusing to allow its MPs a free vote on the divisive issue.
Members of the ruling conservative coalition voted 66 to 33 at the end of a six-hour heated debate to compel members of the government to follow the party line that marriage should be lawful only between a man and a woman.
MP Warren Entsch plans to introduce a bill to parliament on Monday that will allow same-sex marriage throughout Australia, but he and other campaigners concede that that bill will now fail because government MPs will not be free to follow their consciences.
The outcome is a victory for prime minister Tony Abbott, a former Roman Catholic seminarian who has been described as Australia's most socially conservative prime minister in decades.
But a vote on the legislation could damage his leadership if government members broke ranks to support gay marriage.
Mr Abbott declined to say whether he would now allow the legislation to be voted on. MPs in the opposition centre-left Labor Party will be able to decide for themselves how they vote on same-sex marriage.
Mr Abbott extended an olive branch to marriage equality advocates, offering to allow the public to vote on gay marriage in a referendum if his government retains power at elections due late next year.
"Obviously the fact that we are disposed to put it to the people in the next term of parliament shows that we are open to change, but please let's not underestimate the magnitude of this as a cultural shift," he said.
Marriage equality advocates argue that parliament is out of step with the Australian community, with opinions polls showing majority support for same-sex marriage.
Some television networks have refused to carry anti-gay marriage advertising for fear of a viewer backlash. MPs returned to the national capital Canberra this week after a six-week break to see the city's airport illuminated with rainbow colours.
The Snow family, which owns and operates the airport, has joined hundreds of Australian businesses in demonstrating support for marriage equality.