The three construction unions - Ucatt, Unite and GMB - decided to "reluctantly" accept a pay increase last month of between 1% and 1.25% for the lowest paid builders.
But the agreement is now in doubt again after leaders of the National Employers for Local Government Services said the deal was conditional on unions dropping non-pay related claims.
The move has infuriated the unions who are now demanding another meeting with the employers which could place the whole agreement in jeopardy.
The latest wrangle means workers may not see any pay increases before Christmas on a deal which will have to be backdated until April 1 2009 when a new pay offer was due to come into effect.
ADVERTISEMENTUcatt general secretary Alan Ritchi said: "This is totally unacceptable. The employer's side are insisting that the unions abandon negotiations on the non-pay elements of the claim before the agreed pay increases will be implemented.
"There was a binding agreement between us on the question of pay. Attempts to renege on the agreement amount to a breach of contract and an example of bad faith."
An employers spokeswoman said: "While we are pleased the union side has accepted the pay offer we are not prepared to reconsider our position with regard to the non-pay related elemnts of the claim."
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