More than 2000 union delegates have descended on Melbourne's Town Hall for their first mass meeting in 20 years as part of a national call for improved job security and pay.
The hall's 1600 seats filled quickly on Tuesday morning, reaching standing-room only, while more people were stuck outside the meeting, which started with a thunderous chant of "stand up, fight back".
"We are drawing a line in the sand right here today, making a stand; we do not want to see people thrown out of their jobs, facing a 30 per cent pay cut," ACTU secretary Sally McManus told reporters.
"If we let that happen as working people, we'll end up like the working poor of America."
The delegates are developing a plan of action for a union-wide Change the Rules campaign to improve conditions for workers and strengthen union powers.
The Melbourne event is the first of more than two dozen meetings and rallies across Australia during the next month, some to coincide with May Day.
After the meeting, the crowd is due to march to the Southbank offices of Esso/ExxonMobil to rally with workers who have been locked out by the company for 300 days over a bitter pay dispute.
"We are a testament to how broken these rules are," former maintenance worker Troy Carter said.
"Last year 230 families had their lives turned upside down when we were sacked and offered our jobs back the very next day on a 40 per cent pay cut, on rosters that would see us at work at the discretion of the company.
"I've got two young kids and if we don't stick up and fight for them now, far out, it's just a dissemination, it's a race to the bottom."
Change the Rules is the biggest union campaign since the "Your Rights at Work" effort in 2007, which targeted the Howard regime's Work Choices policy and is credited for his government's demise.
Meanwhile, the ACTU is still waiting for the Fair Work Commission's decision on the latest minimum wage increase, which would take effect from July 1.