Councils in England fear they will be left with a big hole in their care budgets because three stopgap funding pots are due to end next year.
Local government leaders warn they will have to start scrapping services within weeks unless extra money arrives in next week's government spending plans.
Nearly £2.4bn of the £16.6bn set aside this year for services for the elderly and disabled comes from the three short-term funds.
But they are due to close in March.
The biggest source of temporary funding is the Better Care Fund, that was set up to encourage joint working between councils and the NHS.
It is worth £1.8bn to councils this year and pays for a variety of different services, including care home places and emergency care teams to support people at home.
Councils are warning these services would be vulnerable unless the government acts.
The other two smaller pots are one-off funds that were set up to plug gaps while the government came up with plans to reform the entire system of social care funding.
It was envisaged those reforms would be in place by now, but they have been delayed numerous times.
Councillor David Williams, of the County Councils Network, said: "We are in the dark over whether this lifeline for care services will continue."
He said councils would "reluctantly" have to start giving notice on contracts they have with agencies to provide these services soon, unless ministers act next week.
Gary Fielding, of North Yorkshire County Council, said he was "deeply worried".
His council has used the temporary funding to set up a discharge hub to help get patients out of hospital quickly as well as a team of "living well" co-ordinators to support frail older people to prevent them going into hospital.
"We're not quite sure what plans to make. If this money is not there we're going to see some significant service reductions," added Mr Fielding.
A Department of Health and Social Care spokesman said funding for care would be revealed in next week's spending announcement.
Chancellor Sajid Javid is due to unveil the plans on Wednesday.
The spokesman said plans to reform social care funding - it is means-tested so some people end up with huge bills - would be revealed in "due course".