Unite unionmembers have voted by three to one in favour of joining the public sector pensions strike on the 30th of November, the day after George Osborne's Autumn Statement on the economy. The vote means all the major unions have voted to take industrial action on the same day, in what has long been billed as a day of co-ordinated strike action over changes to public sector pensions.

The turnout in the Unite strike ballot was 31% - slightly higher than than the ballot of Unison members which was announced two weeks ago, which saw 28% of members taking part. That ballot was billed as the largest in British trade union history. The GMB and the National Association of Probation Officers have also voted to take part in strikes.

The relatively low turnouts among the big unions will lead to further pressure on the government from Tory MPs to introduce a law to make strike action dependent on a minimum threshold of turnout.

However Unite union's vote means more than 3 million people could stay at home on the 30th of November. Thousands of schools are expected to be closed, and significantly the National Association of Head Teachers will to join their employees in industrial action - the first time the headteachers union has voted to strike in its history.

The dispute is over changes to public sector pensions, which will see workers paying in more in contributions and retiring later. The government accepted the findings of the Hutton report, which called for the retirement age for public sector workers to be raised. Unions believe the changes are unfair because they will see the value of pension pots for many middle-aged workers fall dramatically.

At the weekend the Cabinet Office Minister Francis Maude suggested union workers should strike for just 15 minutes, meaning they would not lose a day's pay.

A fortnight ago the Chief Secretary to the Treasury Danny Alexander outlined an 8% increase on the government's previous public sector pension settlement, adding that no worker within 10 years of retirement would need to worry about their own contributions going up.

But this revised package was rejected by the unions, with PCS leader Mark Serwotka saying the latest concessions were only marginal and would still force public servants to pay more in and work longer for less in retirement.

Negotiations on changes to public sector pensions have been going on since February 2011. Those talks appear to have broken down in the past two weeks, with the government's offer being billed as a "take it or leave it" concession. However Westminster insiders believe the government may offer further concessions . These are unlikely to come this side of the day of co-ordinated action on the 30th of November, however, because the deadline for finalising the pensions package for public sector workers comes a month later.

The government may wait to see how many workers actually go on strike, in light of the relatively low turnouts in the ballots organised by unions. The unions themselves were thought to be divided on whether to settle with the government's revised offer from the start of this month, with Brendan Barber, the TUC leader, apparently in favour of softening the union's line.

Other union leaders were reported to have rejected any reconciliation, in favour of holding out for a better deal.