Nurses, teachers and police are among tens of thousands of people expected to walk off the job in a nationwide day of protest, with mass rallies to be held in Melbourne, Sydney, Perth, Brisbane, Launceston, Adelaide, Darwin and in regional centres to mark three months since the beginning of the federal laws.
ACTU president Sharan Burrow will address an expected crowd of many thousands in the Bourke St Mall, Melbourne, while ACTU secretary Greg Combet will attend the Brisbane rally.
An ACTU spokesman said major speakers at the rallies would focus on the human cost of the IR laws, such as unfair sackings which, the unions say, have already occurred, and changes to work contracts that have cut the take-home pay and employment conditions of many workers.
Federal Workplace Minister Kevin Andrews said most workers will choose not to join today's mass protests against new industrial relations (IR) laws.
Speaking on ABC radio, he voiced concern about employee absenteeism during the rallies, saying that if workers wanted to participate they should do so during their lunch break or take pre-arranged unpaid leave.
"There are ways in which people can meet their lawful obligations and still also protest today," Mr Andrews said.
"The reality is that most people are not going to do it because they know that we have delivered, as a government, a period of relative prosperity in Australia.
"Part of the way we have done that has been to have the courage to engage in the reforms so we can meet the challenges of the future," he said.
Australia Post has threatened disciplinary action over unauthorised absences.
Australian Industry Group chief Heather Ridout said that if employees had not been granted leave for the rally then they should be at work.
Federal Opposition Leader Kim Beazley says anger over workplace reforms could push the federal government out of office at the next election.
Mr Beazley told Southern Cross Radio the federal government did not understand how important penalty rates - which were not protected under the new IR legislation - were for middle-income families trying to pay off mortgages.
ACTU secretary Greg Combet said he expected people to use the day to voice their opposition to the Work Choices legislation.
”We've seen these AWAs ... being used to rip off people's penalty rates, public holidays and the list goes on."
Mr Combet has also said reports he wants the unions to control Australia had been grossly exaggerated and taken out of context.
He was quoted earlier this week in a newspaper report saying he would like to see a return to powerful unions.
"Well, of course, it was a joke I was having with five or 600 people at a rally," Mr Combet told ABC radio.
"I was making the joke because of the fact the Liberals have got no argument other than to carry on about union power," he said.
Meanwhile, a survey by the Australian Institute of Management has revealed many businesses and employees knew little about the Work Choices changes.
The survey found that 62.5 per cent of survey respondents had little to no knowledge of the laws.
Sixty-six per cent of the 1,428 company executives, managers and employees polled said the reforms would have a negative impact on employee job security while 61 per cent felt there would be a negative impact on their wages.
About 70 per cent of people said the changes would make them more selective of future employers.