The TUC annual congress has condemned Tony Blair's decision to go along with the US-led war against Iraq, as union criticism of the government continued.
Blair dined with union bosses on Tuesday evening
The motion, unanimously backed by union delegates in Brighton, also opposed any further American attempts at regime changes in states such as Iran, Syria, North Korea and Cuba.
But the TUC stressed its support for the work of British troops in Iraq, many of whom are union members.
The vote came after a top trade unionist called on Tony Blair to "review his position" as prime minister in the wake of the conflict.
Tony Woodley - general secretary elect of the Transport and General Workers' Union - was speaking at the start of a debate at the TUC annual congress on international affairs.
The third day of the congress also saw more union attacks on the government's plans for foundation hospitals.
Mr Woodley's Iraq call, repeating comments made at a fringe meeting earlier this week, went much further than that of his fellow union bosses.
He went on to condemn what he said was a "witch-hunt" against George Galloway, the MP who is currently suspended from Labour over his outspoken position on the war.
The war had led to the "unacceptable and needless deaths of Iraqi children", he said.
Mr Woodley predicted the situation in Iraq would "get worse", adding that the message should go out from this year's TUC conference that there should be "no return to the days of colonialism".
The incoming T&G leader was followed on to the platform by RMT general secretary Bob Crow, who said: "Instead of pouring billions into a war against the people of Iraq we should be using the cash to fund our public services properly.
"The government's excuse for invading Iraq has been exposed as a tissue of lies," said Mr Crow.
"Over-egged, sexed up or exaggerated - whatever words you use, it's quite straightforward: Blair took us to war for oil, and he lied to us about the weapons of mass destruction."
Roger Lyons, joint general secretary of Amicus, said it was time for the United Nations to be given a "genuine role" in the wake of the conflict in Iraq.
"Even American hawks are coming round to the realisation that it is necessary to build peace so as to bring security," he said.