Unison has threatened a major campaign of disruption that will involve schools, councils and hospitals if the planned pay freeze isn’t stopped.

The union’s general secretary Dave Prentis, who is to launch the campaign at Unison’s annual conference, said this was “a crucial time for the union”.

He went on: “Unions came into being for the tough times – and this is what we are facing. The union must continue to work together to combat the… coalition’s no hope austerity agenda – including its programme of damaging public service and job cuts.

“The Tory obsession with privatisation is an on-going battle for the union in the NHS and local government as well as creeping into vital local police services.”

Prentis told the Guardian: “I firmly believe that no pay policy can last more than three years and we will make sure that this policy breaks in the third year.

“I can foresee at some stage that unless the coalition changes tack we will move to industrial action. We are already talking to other unions about a united front. We are never stronger than when we take action together and we will work through the TUC to establish that united front.”

Prentis added: “We will work with other unions and we will generate the strength of feeling that will make people sit up and listen. And if that means that eventually we move to industrial action we will have no hesitation but to move to industrial action.”

Calling the Labour leader Ed Miliband’s and shadow chancellor Ed Balls’s backing for pay restraint “naive in the extreme”, the Unison head said: “If they continue with that stance there is no way whatsoever that our members will vote Labour and the sooner they open their eyes to this the better.”

• Unison has warned Sefton Council and a new ‘free school’ that they face a legal challenge over their “botched” handling of the closure of two local schools, replacing them with the Hawthorne’s Free School.

Around 100 dedicated school support staff and teachers are set to lose their jobs when the two schools in Sefton – St George of England High School and St Wilfrid’s Catholic High School – close later this year and are replaced by the new free school. Staff are caught in the middle of a battle between the council and the new free school, over whether or not they have the right to transfer their jobs across, the union said.

And in a “double hit”, many teachers and support staff are threatened with receiving no redundancy pay. The last act of the chair of governors at St George of England before his resignation was to write a letter to staff informing them that they would be dismissed without their legal entitlement to redundancy, Unison said, pointing out that he is also chair of the new free school trust.

The union’s head of education Jon Richards said: “The council’s botched handling of these school closures is a disgrace. Not only are local schoolchildren and parents facing uncertainty, dedicated school support staff and teachers are facing the dole queues in a dismal jobs market. To pile on more misery by taking away their redundancy pay is a further bitter blow for families in these tough times.

“We are warning Sefton Council and Hawthorne’s that Unison will issue a legal challenge unless this situation is resolved, These dedicated staff should be allowed to carry on working.”