Calls have been made to ban landlords who got tax breaks to buy properties from selling the homes, unless they keep tenants in place.
Housing minister Darragh O'Brien is under pressure to urgently act to address the rental sector as the number of properties available to tenants plummets.
Private tenancies fell by 7,000 in the first nine months of last year alone.
Sinn Féin believes that 20,000 rental tenancies have been lost in recent years as so-called accidental landlords sell up and exit the market.
Calling on Mr O'Brien to carry out an urgent review of the sector, Sinn Féin's housing spokesperson Éoin Ó Broin said the "disorderly exit" of landlords is severely impacting renters.
"My view is if you've got a Section 23 tax break to be the landlord, you should not be allowed evict your tenant when you are selling," he said.
In November, the Cabinet agreed to extend the temporary ban on evictions and a rent freeze for those struggling financially due to the Covid pandemic until at least April.
However, Mr Ó Broin said the contraction in supply is now a major concern. He has called on the minister to take action immediately but said that, as of yet, there has been no commitment given.
He said: "For about 20 years, every single year, the total number of rental tenancies registered with the Rental Tenancies Board [RTB] increased right up until 2016 — partly because there were tax breaks during the Celtic Tiger era.
"What happened literally from quarter one of 2017, every single quarter since then — 2017, 2018, 2019, and 2020 — has seen a loss of tenancies."
Mr Ó Broin believes that many properties owned by accidental landlords have returned to positive net equity in recent years and these home owners now want to "get out".
"And of course they suddenly realised that being a landlord is essentially a full-time job, it requires a lot of effort and that's a real problem," he said.
A spokesperson for Mr O'Broin said the minister recognises that 70% of landlords own just one rental property; 86% of landlords own just one or two rental properties, and that Covid-19 has "given rise to financial difficulty for some landlords, as well as tenants".
They said: "There has been a significant contraction in the market. The number of private tenancies registered with the RTB has reduced by 7,000 tenancies in the year to Q3 2020, with a corresponding reduction of 4,754 in the number of private landlords.
"It was necessary for Government to enhance protections for tenants during Covid-19 and the current eviction moratorium is essential to protect all tenants from eviction while their movement is restricted."
The spokesperson said Mr O’Broin is now going work with Finance Minister Paschal Donohoe to "carefully consider and advance" appropriate policy options to grow the rental sector.
They said: "This must be done in a carefully calibrated manner, taking account of the legitimate interests of both landlords and tenants, the constitutionally protected property rights of landlords, and the financial levers available to the State.”