More than 150,000 people have signed a petition calling for urgent action to fix the system that provides care for older and disabled people.
It urges the prime minister "to end swingeing cuts", saying more than 1.4 million over-65s in England have been left without the support they need.
Also, 40 health leaders have written to Boris Johnson to warn adult social care cuts have a knock-on effect on the NHS.
Government says real-terms funding is rising by 8% from 2015-16 to 2019-20.
Last month, on his first day as prime minister, Mr Johnson said: "I am announcing now - on the steps of Downing Street - that we will fix the crisis in social care once and for all with a clear plan we have prepared to give every older person the dignity and security they deserve."
But the letter calls for:
a plan with cross-party involvement
a long-term financial settlement
short-term money to shore up services this year
support for a wider range of people
One of the signatories, Sussex Community NHS Foundation Trust chief executive Siobhan Melia says vulnerable people are facing unacceptable delays in accessing the care that they need "due to a dearth of provision of social care packages.
"This means that NHS teams are caring for people longer than they need to, placing increased demand on community and hospital services."
Adult social care is the support provided for older and disabled people in their own homes or in residential and nursing homes.
Care workers help people with day-to-day tasks such as washing, dressing, eating and taking medication and this regular contact reduces loneliness, helps spot problems early and keeps people out of hospital.
With more people living longer and with more complex conditions, demand for social care is increasing.