It would cost $69m to run a

referendum on "the carbon tax" being proposed by the Australian government. A referendum is expensive - and even more so when not held in conjunction with an election. They fail more often than they succeed. There have been forty-four since 1906 and all but eight of them have failed.
A referendum question has to pass a double hurdle or "double majority". It has to have the approval of (1) a majority of voters and (2) a majority of the states. If the question affects a specific state then it can be a "triple" majority in that a majority of people in that state have to vote in favour of the question being put.
According to some this makes constitutional change in Australia difficult. That may well be so but it also makes it difficult for governments to extend their powers without the approval of the people.
The last referendum was held on the 1st October 1999. The issue of whether Australia should "become a republic" failed to get a majority in all states and territories. The question still comes up with "republicans" saying that the way the question was posed failed to produce the desired result. If the question had been asked in such a way to allow a direct election for a president some say it is likely that it would still have failed - because other "republicans" would not have wanted to see that big a change.
It is however difficult to get a referendum to pass. The Leader of the Opposition has proposed that the government hold a referendum on the issue of a "carbon tax" - a tax on CO2 emissions. In doing so he has put the "independents" (who currently keep the government in power) in a very difficult position. He is asking them to show just how independent they really are.
The government does not have a mandate to introduce the tax. It came into government specifically saying it would not. A majority of Australians are opposed to it - at last count more than 60%. A referendum would almost certainly fail.
Of course governments do not need a mandate for everything they do. It would be impossible to govern if they did. However this is a major issue with major politic and economic implications and very minor environmental implications. It is a matter of much debate. The government does need a mandate for something which will have widespread economic repercussions.
The government does not need to fall over this but it would have to delay introducing the tax and go to the next election with the tax as part of the platform.
The question now will be whether we fail to have a referendum or whether the referendum will fail.