The country's largest property website, daft.ie has been ordered to block any discriminatory advertising from appearing on its website.
The Workplace Relations Commission made the ruling after finding that rental adverts on daft.ie breached the Equal Status Act on the grounds of family status, age and on the rent allowance ground.
These adverts included terms directed towards prospective tenants, which read "rent allowance not accepted"; "suit family or professionals only"; "would suit young professionals" and "references required".
The case was brought to the WRC by the Irish Human Rights and Equality Commission.
The WRC ordered that Daft Media Ltd "refrain from publishing, displaying or permitting to be published or displayed on its website" discriminatory adverts.
It has also directed daft.ie to "develop a methodology to identify, monitor and block discriminatory advertising on its website" based on a list of terms of trigger words and phrases provided previously to them by the IHREC and to be kept updated.
In making its ruling, the WRC rejected daft.ie's contention that it was a 'mere conduit' for online content under EU e-commerce law and also rejected the claim that such EU law provisions rendered Daft Media Ltd immune from the complaint by the commission.
In a submission to the WRC, Daft Media Ltd asserted that it is not an advertiser or a publisher, but that it is an Information Society Service Provider as defined in the EU e-Commerce directive and that it is not responsible for the content of the material that appears on its website.
At any one time, daft.ie lists approximately 70,000 properties for sale or to rent on the site, while 2.5 million unique users visit daft.ie each month.
The success of the business has generated millions of euro in dividends over the years for the co-founders of the business, brothers, Eamonn and Brian Fallon.
The WRC ruling comes after a three-year legal battle between Daft Media Ltd and the IHREC.
In bringing the complaint, the commission undertook a review of the daft.ie website in May 2016 and identified a number of adverts that discriminated on the housing ('HAP'), age and family status grounds of the Equal Status Acts.
The hearing in the case was heard over three days in March and October of last year and 11 January this year.
Daft Media Ltd argued that the IHREC claim refers to three specific adverts and that any finding made can only be made in respect of these adverts and cannot be extended to include all discriminatory grounds.
However, as part of her lengthy ruling, WRC Adjudication Officer Orla Jones found that Daft Media Ltd "has a vicarious liability for advertisements placed on its website by third parties where these constitute a breach of the Equal Status Act".
Commission member Tony Geoghegan, who has been a long-standing advocate for homeless people in Ireland, welcomed the ruling.
He said: "In the context of the current crises in homelessness and housing, this ruling marks a significant step in efforts to curtail discriminatory advertising particularly around rental accommodation.
"The commission is seeing systemic discrimination against people in receipt of housing social welfare payments, against people with families, against those seeking employment and against young and old people.
"Advertisements for accommodation should describe the property available, not people.
"Today's outcome cuts off advertising options for people who would seek to discriminate when advertising rental accommodation."
The Chief Commissioner of the Irish Human Rights and Equality Commission, Emily Logan, also noted the wider impacts of today's ruling.
She said: "This decision also sends out an important signal that online platforms cannot hold the legal line that they are mere conduits when it comes to hosting discriminatory material. Today's ruling makes clear that there is a responsibility attached to hosting such advertising by website owners."
In its submissions to the WRC, Daft Media Ltd stated that already any adverts uploaded to the site that contain terms that have been previously reported as discriminatory are diverted to a queue of pending adverts for review.
Daft.ie stated that "this queue contains a list of advertisements for manual review by a staff member, prior to the advert appearing on our website".
Daft.ie stated that as it cannot prevent advertisers from editing their advert later, it also operates a "notice and take down" policy.
It also pointed out that in the event that an advert has been reported, an email is also sent to the advertiser to remind them of their legal obligations under the Equal Status Acts and should the advertiser update their advert to re-include any discriminatory content, their account will be suspended.
Daft.ie also stated that a rental allowance filter, which previously enabled property searchers to search for properties that accepted rent allowance, was removed in 2015.
Daft.ie told the WRC that it educates advertisers on its site that it is illegal to use discriminatory language in advertisements at the point of advertisement entry.