The council is asking the government to confirm whether it will continue with the Household Support Fund beyond March.
It was set up in winter 2021 due to the cost-of-living crisis and helped Brighton and Hove residents by providing around £4.3 million during the current financial year for essentials such as food and energy bills.
Some of the cash went to community and voluntary organisations such as food banks.
The city council, along with other authorities including Lambeth Council and Southampton City Council, has written to Simon Hoare MP, Parliamentary Under Secretary of State at the Department for Levelling Up, Housing and Communities, over the issue.
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The joint letter said: "The substantial positive outcomes achieved through previous allocations of the HSF since 2021 cannot be overstated, and the discontinuation of this support would significantly impede our efforts to assist the most vulnerable impacted by what is an ongoing cost of living crisis."
Brighton and Hove City Council leader Bella Sankey said: "Hunger is now a scourge of modern Britain.
"We have an unprecedented number of food banks in Brighton and Hove and I’m told by them that demand is increasingly outstripping supply.
"The Household Support Fund has been critical to allow the council to provide emergency food vouchers and other essentials to residents on the lowest incomes.
"If the support fund is discontinued, I fear the consequences and so I am appealing to the government to reinstate it to mitigate extreme hunger and further homelessness."
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