Unison says local authorities face budget cuts of up to 27% and cannot protect their adult care spending.
The King's Fund has predicted that local authority care services will face a funding gap of at least £1bn by 2015.
Helga Pile, Unison’s national officer for social care, said demand for NHS services would escalate as social care users are left without care.
'With stricter criteria to qualify for care and hiked-up charges, people are being priced out of the help they need,’ she said.
The NHS, which itself must save £15-20bn by 2014, will be unable to cope with further demand created by under-funded social care, she said.