Council workers have been "betrayed" over a wage freeze in local authorities in England, Wales and Northern Ireland, a union claims.
Chancellor George Osborne last year promised public servants on less than £21,000 a year would get an extra £250.
The Treasury insists it made clear at the time he was referring to people directly employed by government.
But the GMB said councils should have abided by the "spirit" of his words.
More than a million local council employees have been told they will not get a pay rise this year.
The unions had been calling for a pay increase of at least £250 a year for all salary grades from 1 April - but employers said a £6.5bn funding gap and the cost of maintaining services meant they could not afford it.
The ruling applies to 1.4 million workers - but does not include teachers and firefighters, who are covered by separate pay arrangements.
Brian Strutton, the GMB's national secretary for public services, said his members would be "sickened by the imposition of another year's pay freeze", following below inflation pay rises in 2008 and 2009.
And it would hit some of Britain's "lowest paid and hardest working people" including home helps, social workers, school dinner ladies and refuse collectors.
Mr Strutton said: "With inflation still running high council workers have now had a 10% real pay cut over the past three years leaving many of them in poverty."
He accused Mr Osborne of "reneging on a promise to low paid workers" who he said were under the impression that they would be receiving a pay increase.
"That was clearly what was meant by George Osborne. His promises are not worth the paper they are printed on," he told BBC News.
But he added: "Nobody actually stopped local government from doing something in the spirit of George Osborne's policy. It is local government volunteering to be the worst employers in the public sector."
In his budget speech in June, Mr Osborne said 1.7 million "public servants" earning less than £21,000 a year "will each receive a flat pay rise worth £250 in both these years, so that those on the very lowest salaries will get a proportionately larger rise".
But Mr Strutton said the Treasury had been forced to issue a "clarification" after the speech sparked protests from local government employers, who have always been free to set their own pay levels.
Treasury sources said they had made it clear, in background papers issued with the budget, that Mr Osborne was referring to workers directly employed by the government, not council employees.
But the BBC has seen a letter that was sent from the Local Government Employers to the chief executives of local councils and the Local Government Association which suggests the Treasury had been forced to clarify its position following Mr Osborne's speech - but still expected local authorities to soften the impact of a tough pay settlement on the lowest paid.
"We have clarified the intention of the Government's policy on public sector pay, as announced in the Chancellor's budget statement, and its implications for local government," says the letter from the employers association's chief negotiator, dated 8 July.
It adds: "The Government will expect local government to show similar restraint on pay to the rest of the public sector; it will also expect local government to have regard to the Government's fairness agenda, which seeks to provide the lower paid with some protection from the impact of pay restraint."
'Not taken lightly'
The Local Government Association denied councils had defied the chancellor over low pay - insisting it had always been clear that council workers had a different pay settlement to civil servants employed directly by government departments.
A Treasury spokesman said: "We have always been clear that local government pay remains a matter for negotiation and agreement between employers and unions.
"But we have also made clear that we expect local government to show restraint on pay in line with the rest of the public sector as well as seeking to provide the lower paid with some protection from the impact of pay restraint."
Jan Parkinson, managing director of Local Government Employers, said the decision to freeze wages had "not been taken lightly" and councils were "facing extremely tough choices this year".
The organisation said the pay demands of trade unions Unison, Unite and the GMB would have added 1.23%, or £265m, to the local government pay bill.
When inflation is taken into account, the freeze will add up to a pay cut for council workers, unions say.
A Unison spokesman said "a toxic cocktail of rising cost of living, cuts to terms and conditions, and now frozen pay means council workers are seeing their money vanish before their eyes".
The spokesman added: "70% of council workers earn less than £21,000 and it is a disgrace that even they will not get any help to make ends meet."