The Advertising Standards Authority has said that estate agents must now publish any compulsory fees to be paid by the consumer planning to rent a property in its adverts or materials.
The warning came as the ASA ruled against estate agent Your Move for an advert that appeared on property website Rightmove.
Your Move broke advertising rules by not making clear that non-optional fees and charges – in this case an administration fee – would be added to the quoted price.
Guy Parker, ASA chief executive, said: "Hidden fees are not only unfair, they hit those who are struggling hardest. Our ruling today makes clear that letting agents need to get their houses in order and treat potential tenants fairly."
Parker went on to say that young people and students were particularly vulnerable, adding: "It is now our priority to make sure agents across the sector bring their advertising into line."
Your Move said in a statement: "We strongly believe in the principles of the Consumer Protection from Unfair Trading Regulations 2008, as demonstrated by the fact that we provide applicants with information at a stage prior to them making their decision to enter into a tenancy agreement – the timing of which compliments the Office of Fair Trading guidance for estate agents, and that we have also actively engaged with the regulators, in particular the OFT.
"In view of the findings, however, we will of course be reviewing our approach, and in support of this look forward to the OFT introducing official guidance for the lettings market as soon as possible to ensure greater clarity on matters of this kind."