Birmingham Citizens Advice Bureau is expected to shut down all five of its advice centres after the city council decided to withdraw all its funding, worth £600,000 a year.
The CAB, the largest in the country, said it would have to close all of its advice centres on 11 February with the loss of 45 jobs, unless replacement funding could be found.
"The funding provided by Birmingham City Council allows us to lever in another £2.4m in funding from other sources," said Yvonne Davies, chief executive of Birmingham CAB. "It's the spine of our funding. We can't operate without it.
"Other funders fund us to provide more specialist services based on the basic services that the council money allows us to operate. We are now looking for alternative sources of funding."
She said the council had told her that its own advice centres could provide the same services for the people of Birmingham.
"However, we feel that many people are reluctant to approach the council," she said. "We also have 150 volunteers who provide high-quality advice, and their services will be lost."
The council said it would continue to commission advice services on a smaller scale, but would not begin the commissioning process until August.
A city council spokeswoman said that the council had announced the funding cut on 31 December. She added that the council had made it clear that the CAB should not rely on it for funding.