Proposed cuts to housing benefits could force about 70,000 claimants out of their homes in the West Midlands, the National Housing Federation has said.
It represents 1,200 not-for-profit housing associations in England and said many tenants who privately rented may soon be unable to pay their rent.
Birmingham would be worst hit in the region, with 14,260 claimants at risk.
The cuts are expected as part of a measure to reduce the welfare bill and bring down a £155bn budget deficit.
In the Spending Review on Wednesday the government is expected to propose that housing benefit payments are reduced and brought into line with the bottom third of private sector rental prices.
If that happens, the National Housing Federation (NHF) said there would only be 12,650 homes available at a price the 80,000 housing benefit claimants in the region could afford.
The NHF said that could leave 67,350 claimants unable to afford their current rent, being forced out of their homes.
Paul Williams, NHF West Midlands Regional spokesman, told the BBC's Politics Show in the Midlands that the cuts would hit some of the most vulnerable people in society and increase pressure on councils to re-home them.
"The responsibility doesn't go away for looking after those vulnerable people in society," he said.
"They will go straight to the local authority to be picked up because most of them will have a statutory responsibility," he added.
The proposed changes would affect 80% of those receiving housing benefit, said Sajid Javid, Conservative MP for Bromsgrove and member of the Commons Work & Pensions Select Committee.
But he has rejected claims that it could spark a housing crisis.
"We are not talking about an astronomical difference from what they get today," he said.
"I think it will be a bit silly for people to say just because people on average are getting £9 less a week that they will somehow lose their house and home," he added.