Union bosses have pledged to break the law if the UK Government introduces reforms to union funding and the right to strike.
The Conservatives have devised the Trade Unions Bill, designed to "ensure hard working people are not disrupted by little-supported strike action" by introducing a 50% threshold for strike ballots and allowing union members to opt out of donating to political parties.
Grahame Smith, general secretary of the Scottish Trades Union Congress, and Pat Rafferty, Scottish Secretary of Unite, told hundreds of protesters at an anti-austerity rally in Glasgow that "bad laws" are there to be broken.
The rally also heard from Kirsteen Fraser, SNP Trade Union Group, who said "there is no actual reason" for the UK Government's austerity cuts.
Chancellor George Osborne says his economic plan is necessary to reduce the UK's budget deficit which is one of the highest in developed world.
Cat Boyd, co-founder of the Radical Independence campaign, urged protesters to follow the example of Greece, which is withholding repayment of a 1.6 billion euro loan from the International Monetary Fund (IMF), praising Greek citizens who are "refusing to lie down and submit to slavery".
Denise Christie, from the Labour Party Campaign for Socialism, was heckled as she criticised Scottish Government cuts to the fire service by a protester who went on to clash with a female steward who tried to subdue him.
Mr Smith said: "The Tories talk about outlawing undemocratic strike action. This has nothing to do with democracy or participation.
"I'm all in favour of more people participating in strike ballots. If it was about participation, we should be allowed to conduct secure online ballots or secret workplace ballots.
"This is about the naked self interest of a privileged elite attempting to prevent any organised resistance to its ability and desire to wield its economic and political power unchallenged.
"No one should be in any doubt about our determination to resit.
"It is inevitable if these policies are implemented then they will place unions in conflict with the law.
"We would not be standing here today if our predecessors had not broken bad laws.
"Across the world, civil and human rights have been won and protected only because people have united to break bad laws, and if that's what it takes to ensure unions can continue to represent their members then so be it."
Mr Rafferty said: "Let's get on the front foot and send a loud and clear message to Cameron and his cronies today.
"When you come after us we will fight back. When you create laws to curb our democracy we will break them, and when you oppress us we will organise.
"Comrades, we will show them that there is power in a union - you, me, us, our union - and we will win."
Ms Fraser said: "There is no actual reason for these cuts, there is no basis in economics for these cuts, it's just a full scale attack on working class people."
Ms Boyd said: "All across Europe, people are challenging those who think they have the ability to implement austerity without resistance.
"In Greece citizens are standing up to a political and economic system which has torn apart the very fabric of their society, against the United States, the IMF, the European elites, against all global power.
"The people in Athens just now are refusing to lie down and submit to slavery, and if we can show just a fraction of their heroism against our own elites, against the Bullingdon boys club in Westminster, we can be sure that this government will not last."
Ms Christie said: "I've been a firefighter for 20 years and I have never seen such devastating cuts to the fire service in all my life.
"We've been on the picket lines for our pensions, to stop fire stations closing and to save the fire service.
"We've seen cuts to the fire service of over 400 frontline firefighters and control operators in this last couple of years, and the biggest impact that has is on women - women that work in the control rooms, the cleaning department, the catering department.
"It's an absolute disgrace that women are having to bear the brunt of these cuts."
Ms Christie was interrupted by a protester who called her "a disgrace" and urged her to leave the stage.
"You're a card carrier of the Labour Party, you shouldn't even be here," he said.
"Get Labour out, they're responsible for the cuts."