Trade unions have called a collective day of strike action on 30 November, warning the government that Britain faces the "biggest mobilisation in a generation" unless ministers rethink "hugely damaging" changes to public sector pension schemes.

Up to 3 million public sector workers, including nurses, teachers and careworkers, are expected to take part in industrial action, with at least 14 unions committed to strikes over government pension reforms.

The TUC general secretary, Brendan Barber, said: "The intention will be to take the call for pensions justice for both public and private sector workers to every corner of the land on that day in the biggest trade union mobilisation in a generation."

Barber confirmed that the 24-hour walkout – potentially the biggest since the 1926 General Strike – could signal the beginning of a wave of industrial action as individual unions and groups of public sector workers mounted their own campaigns across the UK.

"Further consideration is being given to what further action may be appropriate beyond the day of action if progress towards a settlement is not secured," he said.

The GMB union, which has more than 300,000 public sector members, has warned that the action could spread into next summer, hitting the London Olympics and the Queen's jubilee.

The country's three largest trade unions – Unison, Unite and the GMB – announced their decisions to serve notice of ballots over pension reforms at the TUC conference on Wednesday, calling for strike action to be co-ordinated in an attempt to maximise pressure on the government.

Plans are being drawn up for sustained action in tactical and "smart" strikes, which would target specific services and could have an immediate impact without affecting vulnerable groups.

Brian Strutton, the GMB national secretary for public services, said after the debate: "We are talking about throwing everything at it that we can, rolling into next summer.

"We are not just looking to nudge this along. We are assuming that this will be a huge set piece conflict running for a long time."

Downing Street said the ballot announcements were "disappointing", adding that taking industrial action in the current financial climate would be "irresponsible".

David Cameron's official spokesman said: "Our view is that the best way forward is to continue with talks, and we have always been very clear that we should try to have a constructive dialogue with the unions.

"Clearly, it is disappointing that there have been calls for industrial action, particularly as the talks are still ongoing.

"On pensions, we have been very clear about the need for reform, but we have also been making the point that, even after these reforms come through, public sector pensions will still be among the very best available."

Cameron's trade union envoy sat in the TUC conference audience as unions described the pension reforms as an "unprecedented attack on ordinary people".

The collective public sector membership of Unison, Unite and the GMB is 1.65 million. Together with other unions in the process of balloting, co-ordinated action could involve up to 3 million public sector workers.

The move puts Labour-affiliated unions on a collision course with the party's leader, Ed Miliband, who told TUC delegates on Tuesday that strike action on public sector pensions was "a mistake".

The Prison Officers Association warned it was ready to defy the strike ban covering the service "if there is no deal to be found in negotiations".

The firefighters' union also declared that it was taking steps towards industrial action, while other unions used the conference platform to affirm their readiness to join sister unions in a mass walkout.

The NASUWT teaching union is among other unions preparing to ballot almost 250,000 members.

Patrick Roach, its deputy general secretary, said: "The attack on pensions is only one element of the assault on ordinary working people, on the public sector and on the welfare state.

"Be in no doubt – we are in the midst of a perfect storm. A perfect storm of assaults on pay, on jobs, on rights at work, as well as on pensions. That is why the NASUWT has committed to ballot its members for industrial action this autumn."

Dave Prentis, the general secretary of Unison, the country's largest public sector union, kicked off Wednesday's conference session by giving formal notice of industrial action ballots to 9,000 employers.

He said striking was the "last thing" members wanted to do, but the time had come to make a stand against government attempts to get its "pound of flesh" from workers by seeking to bring in new pension schemes with "far worse benefits".

"We've been patient, we've co-operated – but there comes a time when we say enough is enough because, if we don't, they'll be back for more," he said.

"It's a decision we don't take lightly and the stakes are high – higher than ever before."

Prentis rounded on the government for seeking to take the pensions of ordinary workers on low pay who had saved for their old age "every week of their working lives".

Gail Cartmail, the assistant general secretary of Unite, told the conference: "When the coalition came to power, we knew we faced the fight of our lives – we knew they would seek to weaken and divide us.

"While we will never walk away from talks, neither can we sit on our hands. We will support days of action and tactical selective action."

Paul Kenny, the GMB general secretary, said after the debate: "If Francis Maude [the minister for the cabinet office leading the pension talks] thinks everything is going to be all right, he had better get into practice in emptying rubbish bins and sweeping the streets. He is going to have plenty of work to do."

Barber told delegates: "This morning's debate has shown immense unity of purpose. We may yet need to show that unity in further action, and let no one doubt that our resolve and determination to win fairness and justice is absolute."

Len McCluskey, the Unite general secretary, said: "Hopefully the government will see the anger and perhaps take a step back, be a little bit more flexible and less intransigent."