Thousands of rented rooms could be removed from the housing market because of a new registration scheme.
Tory councillor Peter Lewis told Brighton and Hove City Council more than 46 properties had already been removed from the private rented sector since the registration scheme started at the beginning of April.
He said the Southern Private Landlords' Association forecasts more than 4,000 rooms could be deemed unusable.
This would lead to more homelessness and increased housing costs for the council.
Cabinet housing councillor Tehmtan Framroze said the registration scheme was in line with Government guidance and supported by some landlords.
The idea was to provide decent and safe housing for private tenants in the city.
Coun Framroze said a close watch was being kept on the scheme and added: "We will know immediately if it is not working.
"There is no evidence to support the allegation of a loss of housing."
Coun Lewis said most landlords agreed that a scheme was needed but it had to be tailored to the needs of the area.
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