Auditors have ordered Northamptonshire County Council not to set its budget this week - because it could be illegal.
The cash-strapped local authority was due to vote on its spending plans for the next year and decide how much to charge tax payers at a meeting on Thursday.
A ban on emergency spending has already been enforced and the council has had to agree to sell-off its new £52m headquarters in Northampton, thanks to a multi-million pound black hole in its finances.
But today, auditors KPMG served a notice on the council telling members that voting on a budget for 2018/19 "would be unlawful and likely to cause a loss or deficiency".
Instead, councillors will have to discuss what to do next on Thursday and push back its budget vote for another week.
Explaining its decision, KPMG called into question estimates made by the council about how much money it would need to spend next year, and where that money would come from.
KPMG said it had already raised concerns about the authority's ability to provide "value for money" in previous years and pointed out: "Since we reached these conclusions, the authority's financial position has significantly deteriorated."
A spokesman for Northamptonshire County Council said it was very much aware of its poor financial situation.