TUC boss Frances O'Grady turns fire on Tories over funding reform plans
The head of the UK's union movement has told David Cameron to take a "long hard look in the mirror" before making changes to political funding laws.
The government wants to put a cap of £390,000 on the amount of money that organisations other than parties spend on campaigning around election time.
But TUC leader Frances O'Grady said the Conservatives could not "shut us up" and unions would defend themselves.
Delegates later voted for a "campaign of co-ordinated industrial action".
The Unison motion, which also calls for zero hour contracts to be outlawed, was passed overwhelmingly at the TUC's annual conference.
The issue of money and politics has dominated the start of the event in Bournemouth.
Several union general secretaries have attacked Labour's Ed Miliband over his plans to scrap the automatic "affiliation fee" paid by millions of union members to the party.
He says this will lead to more people opting to become full party members instead, while his detractors argue this is unrealistic.
But, in her first conference speech since becoming TUC general secretary earlier this year, Ms O'Grady attempted to draw attention to another row, between the unions and the Conservative-Liberal Democrat government.
In July, ministers introduced the Transparency of Lobbying, Non-Party Campaigning, and Trade Union Administration Bill, which would set a £390,000 cap on the amount any organisation - excluding political parties - could spend helping candidates and parties across the UK during elections.
Following opposition from charities and many MPs, the government introduced several changes last week.
The National Council for Voluntary Organisations said its demands had been "significantly met", but the TUC insists the government has not made enough concessions and that freedom on speech could be under threat.
In her speech, Ms O'Grady said: "Whether unions set up a political fund is a matter for members, not ministers, because for too long, politics has been controlled by those who already have far too much money and far too much power.
"Half the Conservative Party's funding comes from the City. One third of its new intake of MPs are drawn from the banking industry alone and we know what happens when the super-rich get to run the tax system."
She added: "In contrast, unions are Britain's biggest democratic membership movement of ordinary people.
"We are already required by law to report our membership records every year. We have more than 10 times the membership of all of Britain's political parties put together. It may even be more. The truth is, we simply don't know.
"Because political parties don't have to account for their members in the way that we have to account for ours. In fact, the Conservative Party refuses point blank to say how many members it has.
"So before he starts lecturing unions about transparency, the prime minister should take a long hard look in the mirror.
"We already publish our numbers. I challenge David Cameron to publish his."
On Friday, the Leader of the House of Commons, Andrew Lansley, indicated the government would not make any further concessions, saying: "I heard what the charities and voluntary organisations had to say.
"While we always were clear that we had no intention of preventing them campaigning on policies and issues as they always have, I wanted the bill to be as clear as it could possibly be.
"So I am very glad that I have been able to meet the concerns of voluntary organisations, while ensuring that the bill still regulates effectively when organisations directly try to promote election candidates and parties."
Ms O'Grady, the TUC's first female leader, said political parties should run on a manifesto promising decent jobs, full employment, a million new council and affordable houses, fair pay and workers' rights, and an NHS run for the people and not for profit.
She urged activists to "roll up their sleeves" and influence Labour policy in the run-up to the 2015 general election, rather than accept a "vanilla version".
Ms O'Grady, who was given a standing ovation, added: "I want to challenge politicians of all parties to tell us where they are [on issues]."
She also said: "For trades unionists to argue that voting is a waste of time is a danger, one that puts us into the hands of our opponents."
The Congress will debate issues including pay, jobs, welfare and anti-austerity campaigning.
Labour leader Ed Miliband will give a speech on Tuesday, while his deputy, Harriet Harman, will meet union leaders at a private dinner on Monday night in an effort to relieve tensions.