Tax information on landlords could be provided by tenants, following HMRC's step to directly ask them to act as informants.
The Revenue has identified private-rented homes owned by landlords or offshore companies, and wants to check the correct amount of tax is paid on rental profits.
It seems particularly interested in gathering information on non-UK resident landlords, properties owned in trust, and any details of trustees.
The Chartered Institute of Taxation (CIOT) said the letters threatened tenants with fines if they failed to deduct income tax from the rent they pay.
Brian Slater, chair of CIOT's property taxes sub-committee, said:
"A tenant may not know that the landlord's usual place of abode is outside the UK and, even if they do, how will they know about their tax obligations?
"The wording at the end of the letter about errors and penalties could also alarm the recipient, especially if they are not able to answer all the questions.
"There is no legal obligation to respond to the letter and questionnaire, but a response will enable HMRC to find a resolution."
Talk to us about your tax status.