The Vale of Glamorgan Council has prosecuted 30 landlords over the past five years.
This comes as a report by Public Interest Lawyers found that more than 100 councils in England and Wales did not take any landlords to court between 2019/20 and 2023/24.
The Vale of Glamorgan Council's prosecutions - after 6,874 complaints - included a £37,000 fine for Nazir Ahmed in February 2024, after an investigation found a rodent infestation and the electricity supply to the entire property being shut off.
Another landlord was fined £68,295 for failing to obtain an HMO licence.
Reacting to the report, Tom Darling, director of the Renters’ Reform Coalition, said: "These are worrying findings.
"The key problem councils face here is ultimately a lack of resources, after years of rising costs and shrinking budgets.
"We’ve called on the government to provide local authorities – who will have the crucial role of enforcing the forthcoming Renters’ Rights Bill – with the additional funding and guidance they need to protect renters from rogue landlords."
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