Homeowners who have rented out rooms to tourists using a well-known website will now have their details handed over to the Revenue Commissioners.
An estimated 9,000 householders have rented on Airbnb.
The taxman is planning to go after those who haven't declared this rental income. The clampdown will be backdated to May 2014.
The website is usually used for short-term letting of rooms or houses by tourists. As a result, the rents charged per night tend to be higher than the normal private rented sector.
The website has informed its customers it will be handing over details of customers who hosted visitors and the amount of income they earned. As the rent is paid through the website, Airbnb knows exactly how much was paid. The clampdown will also focus on rent earned by people with foreign properties.
Revenue had warned homeowners about tax evasion on rental income earlier this year.
The taxman made it clear that the rent-a-room scheme, which allows people to earn up to €12,000 tax-free a year, cannot be used for relief on short-term lets to guests.
Airbnb, whose European headquarters is based in Ringsend, Dublin, has emailed "hosts" in Ireland to explain they have a "legal obligation" to report earnings to Revenue.
Currently, there are more than 1,000 rooms or properties in Ireland advertised on the website.