Disability charities have urged ministers to "end the uncertainty" around future funding for supported housing for disabled people who want to live independently.
The 15 charities wrote to the Government, calling on it to set out what would happen to housing benefit rates for the supported housing sector from 2018 onwards.
Earlier this year, the Government announced a one-year exemption for the supported housing sector from a planned 1% reduction in rent.
It also delayed for 12 months the introduction of the local housing allowance (LHA) cap - which affects residents living in supported housing.
The Government has commissioned a review into the impact of its proposals but the charities warned that 40% of existing supported accommodation would be at risk of closure if the allowance cap went ahead.
Fears have been expressed that the changes would reduce the amount of money supported housing providers receive in rent and could make it more difficult for them to deliver specialist services.
Mencap chief executive Jan Tregelles, who signed the letter, said: "The pressure on supported housing is already immense, with at least 900 more supported homes required every year for people with a learning disability alone.
"The recent Government announcement of a cap on housing benefit rates for supported housing has created an uncertainty that has forced providers to put on hold plans to buy or build new properties, and which is likely to turn this pressure into a crisis."
"It is now key that the Government does their part and offers the certainty the sector desperately needs.
"We urge the Government to provide this by removing the threat of the LHA cap and by creating a sustainable long-term funding structure for supported housing going forward, so people with a learning disability can live independent lives and access their community."
The letter was signed by the bosses of Mencap, Mind, Sense, RNIB, National Autistic Society, Papworth Trust, Leonard Cheshire, Inclusion London, MND Association, United Response, Deafblind UK, Dimensions, Ambitious about Autism and the Housing and Support Alliance.
A Department for Work and Pensions spokesman said: "We fully support the valuable work carried out by supported accommodation providers.
"That is why we deferred this measure for this sector while we conduct a review to ensure it is sustainable in the long-term.
"We will continue working with providers to ensure the right protections are in place and will set out our plans for reform in the autumn."