Almost 17,000 landlords have left the private rental market in the past three years.
Their exit means that hopes of pressure easing for renters facing scarcity of supply and high rents may be short-lived.
There was an expectation that short-term holiday rentals would be converted to long-term residential leases because of new regulations and the coronavirus crisis.
That has yet to happen to a significant degree and, with optimism building that the holiday season could be saved, there is less incentive for making the switch.
The Residential Tenancies Board (RTB) is carrying out surveys of landlords who have de-listed their properties to try to find out why.
Sinn Fein housing spokesman Eoin O Broin, who obtained the figures, said he believed most were either part-time landlords who bought an investment property during the boom and quickly fell into negative equity, or else accidental landlords who could not sell their home when they had to move for work or family reasons.
"Once house prices started to return to positive equity from the start of 2017, and they could walk away debt-free, they started to exit," he said.
"The real problem is that many of these properties are the properties where families have been issued vacant possession notices to quit.
"So it's not just that we're losing properties, but these are the properties where the families who are ending up homeless are coming from."
The RTB figures show there were almost 320,000 private tenancies registered at the end of 2016, but just 303,000 at the end of 2019.
Around 7,000 de-listed last year alone, but Mr O Broin said the number could be greater as new entries from the build-to-rent sector were masking the problem.
"The difficulty with these properties is that they are at the high end of the market, in a different price range, and are not a replacement for the kind of homes that modest-income families under notices to quit can afford," he said.
Rents fell by 2pc in April, according to property website Daft.ie, but with rocketing unemployment, modest cuts may not be enough to help renters.
"The concern is that if rent arrears rise, more landlords will opt to get out and that will only accelerate the exit," Mr O Broin said.
Pressure is growing on the Government to extend a temporary ban on evictions and rent increases, which is due to expire on June 27.
Housing Minister Eoghan Murphy has commissioned an expert report on the likely fall-out from the crisis for the rental sector.
He told the Dail he expected a debt arrears problem and said it was in the interests of both renters and landlords to handle it correctly when it arises.