The learning disability sector looks set to be pursued by HMRC for an estimated sum of £400million from next Monday, October 2.
The Government have so far rejected appeals to finance the debt which tribunals have ruled is owed to sleep-in carers who worked shifts over the last six years.
“Government needs to recognise that only a fully funded solution will work," Mencap Chairman Derek Lewis said.
"Partial funding would see scores of small and medium sized charities and family run firms go to the wall as they quickly became insolvent. The damage will have been done."
"Securing the future of learning disability care across the UK would be the true hallmark of a Government that is committed to fairness and building a country where no-one gets left behind".
The Government have not commented since promising to "look carefully" at the issue earlier in the summer.