A spokesman for the 'Stop the War Coalition' says today's demonstration in Sydney is designed to focus the public's attention on the possibility of an invasion of Iran.
Jervis Ryan says that the possibility of war with Iran is real and he wants the prime minister, John Howard, to rule out supporting the United States if it decides to invade Iran.
There has been escalating global tension over Iran's nuclear-weapons ambitions and the United States has refused to rule out military action if the Iranians fail to cease uranium enrichment.
Mr Ryan says he does not want Australia to follow the same path as the one it pursued in the lead-up to the invasion of Iraq.
"We have to learn the lessons of history and we have to look at Iraq and realise that they pretended to be going through diplomatic procedures but the information that emerged subsequently showed that they had made the decision to go to war eight or nine months before it actually happened and the weapons inspections and the diplomatic process, it was all a charade."