An organisation tracking internet ads related to the referendum on the Eighth Amendment says they are still appearing online, despite a ban on all such ads by Google and a ban on overseas ads by Facebook.
The Transparent Referendum Initiative (TRI) said members of the public have sent on screen grabs that suggest large scale political targeting is still happening across a range of websites and platforms.
But the TRI said it cannot tell who is posting or delivering the ads because there was no means of tracing them.
The initiative was set up to shine a light on the unregulated nature of online political advertising in Ireland.
It is using a desktop web browser plugin that has been installed by more than 500 volunteers to gather ads connected to the referendum that are appearing in users News Feeds on Facebook.
It said the volunteers make up a reasonably representative sample when it comes to age and gender, although it is more heavily weighted towards people living in Leinster.
The group is working with the Geary Institute in University College Dublin to analyse the data and today it released some preliminary findings.
The organisations began tracking the ads in February and say that since then almost 900 ads have been identified.
However, the researchers say this is probably only a snapshot of the ads being deployed by individuals and campaign groups.
There has been a sharp increase in the volume of ads posted since 22 April, with 230 new ones gathered in the past week alone.
The study has found that the ads are coming from 224 unique pages on Facebook.
It found 43% of these advertisers are registered or affiliated with the Standards in Public Office Commission, but the other 57% are not.
The data shows that 78% of the ads are of Irish origin, with 13% coming from overseas and 9% untraceable.
Ads have been gathered from US, Canadian and European based organisations amongst others.
The researchers have also seen seven groups that are purporting to provide neutral information on the referendum, but which are actually offering biased information towards one side or another.
In total, 28 ads of the total of 888 are from such groups.
TRI Co-founder Liz Carolan called on Google and Facebook to make public now information about their decisions to ban referendum related ads.
She said there was still time for transparency on what has happened ahead of the vote on 25 May.
She also repeated TRI's call for legislative changes to ensure better transparency around who is paying for political online ads here, how much they spent and who they are being targeted at into the future.
A spokesperson for Google said that it would not be able to comment on the claim by the Transparent Referendum Initiative that referendum ads continue to appear online without seeing evidence that this is the case.
A Facebook spokersperson said the company knows its ads policy is working as it has rejected and removed a number of foreign ads since the ban was introduced.