The Labour Party set up a polling company which sent members out in Dublin to survey voters, thecan reveal.
Irish Scientific Surveys was set up during the 1990s by former TD Pat Upton and a previous director of elections Niall Connolly, who are both listed as directors, with its purpose stated as "public opinion polling".
Thehas spoken with a number of sources who have confirmed the practice.
One former member in Dublin south-central, said during the 1990s members were given fake identity cards to use when carrying out the survey.
"People would go out and knock on doors with ID from that company and a sample ballot paper, and we would ask who would they vote for," he said.
"The purpose was to gauge the strength of the party, whether we were actually getting through to people.
"The pure purpose of it was for Labour, and it was all members who were sent out.
"We'd go to hundreds of houses, and it was conducted several times throughout one period, usually around six months before an election, a sample was a minimum of 200 to 250 houses, chosen at random.
"Sometimes we'd test the ground for other candidates, in local elections or whatever.
"You were to say you were from Irish Scientific Surveys and tell people on the doors you didn't know who the client was."
The party denied last week that it had ever conducted polling in this manner.
A spokesperson said: “The Labour Party have no knowledge of this whatsoever.”
When asked if fake pollsters were ever used by Labour, a spokesperson said: "Not to our knowledge or with the sanction of our head office.”
Mr Upton, who died in 1999, was elected to the Dáil in 1992 and in 1997.
Fine Gael, Fianna Fáil, Sinn Féin and the Green Party have all admitted to using the practice in the last week.
All now say the practice has ended.
Tanaiste Leo Varadkar's campaign previously gave students fake business cards with the name Political Research Association of Ireland to show at the doors if asked to identify where they were from. Minister for Foreign Affairs Simon Coveney has also admitted that the practice was carried out in his constituency. The party say the practice ended in 2016.
Fianna Fáil says its practice of using fake pollsters ended in 2007 before Taoiseach Micheál Martin was leader. TD Marc MacSharry has called on the leader to resign and has written to the Garda commissioner.
The party say there were "isolated incidences of this taking place in some constituencies over a decade ago". MEP Ciaran Cuffe admitted he used a fake research company name to canvass voters.
Sinn Féin members went door to door wearing fake ID badges stating they were from a market research company. They were told to tell voters the Irish Market Research Company for one day of work. The party says it ended around 2016.
Paul Murphy has said he carried out covert polling before he was in People Before Profit, which has not used the practice.