Unison members will be asked to strike on November 30, with the prospect of further action, including a rolling programme of stoppages.

Mr Prentis said essential public services will be protected on strike days.

Other unions are also balloting workers, raising the prospect of a strike by millions of workers on November 30.

Mr Prentis said the strike in November will be the biggest day of industrial action ever held in the UK.

Unison said 9,500 separate employers were involved in its dispute and Mr Prentis said he was expecting some to mount a legal challenge to the ballot.

It is the first time Unison has balloted its entire membership for industrial action.

“We are doing everything possible to get a high turnout and we are confident of a big ‘yes’ vote,” Mr Prentis told a news conference.

“This is a fight not just about whether it is right to increase contributions, but it’s a fight for the survival of public service pension schemes.”

Mr Prentis said Unison was not prepared to sit back and see contributions increase, retirement age rise and pensions fall.

Unions have been talking to the Government for eight months over pensions, but Mr Prentis said “very little progress” had been made.