GMB became the third union to call strike action for July 10 yesterday after members voted by three to one in favour. 

More than 26,000 members voted to fight the Con-Dems’ public-sector pay freeze compared with 9,000 who voted No in a ballot carried out by the Electoral Reform Society. 

It means GMB members will join over a million local government and school workers in England, Wales and Northern Ireland from other unions in the massive summer walkout. 

The National Union of Teachers and Unison have already named the date for action over another below-inflation pay offer. 

And the total number of workers striking on July 10 could exceed two million if a majority of Unite members have voted Yes when the union’s ballot result is announced at its conference on Monday. 

Civil servants’ union PCS is also balloting members on support for the strike. 

GMB national secretary Brian Strutton said David Cameron’s unpopular Con-Dem coalition could face the second-biggest dispute ever.

He said: “Our members have spoken loud and clear and said they want to go on strike. 

“Members serving school meals, cleaning streets, emptying bins, looking after the elderly, helping children in classrooms and in all the other vital roles serving our communities are fed up with being ignored and undervalued.”

The Star understands a massive demonstration is being planned by trade unions for the day of the strike. 

Hundreds of thousands of striking workers and supporters are expected to march from the BBC’s Broadcasting House to Trafalgar Square for a huge rally.