SINN Féin has not responded to queries about whether its internal voter database also includes Northern Ireland.
The Republic's Data Protection Commission has written to the party asking for information on how it uses Facebook to target voters on the electoral register.
It is understood Data Protection Commissioner Helen Dixon has asked whether voters are aware about how their information is being used.
Sinn Féin uses its own searchable digital electoral register database, Abú. The database includes the names and addresses of millions of voters and predicts how they will vote.
However, it remains unclear if the database also extends to Northern Ireland.
The Irish News asked the party whether the database holds information about voters in Northern Ireland elections.
Sinn Féin had yet to respond yesterday.
According to reports in the Sunday Independent, people attending an internal Sinn Féin training seminar were urged to identify and engage with voters by cross-referencing data from Facebook with the party's own Abú database.
Attendees were told "Facebook is king".
"We can confirm that we have received correspondence from the Office of the Data Protection Commission," a Sinn Féin spokesperson told RTÉ.
"We look forward to engaging with them."
Tánaiste Leo Varadkar said Sinn Féin leader Mary Lou McDonald must urgently address questions about the party's internal voter database.
He said it was "a good thing" the Data Protection Commissioner was examining the issue but added that "it would be helpful" if Ms McDonald answered questions.
Fine Gael Senator John Cummins has claimed Sinn Féin had a "litany of unanswered questions" about the database.
"Sinn Féin are accustomed to remaining silent on the party's lack of transparency and finances, but this latest development is something the party cannot remain silent about as it could potentially deal with a serious data breach of voters' personal information," he said.
"The leadership of Sinn Féin must now reveal where this online database is stored and who exactly are the people being asked to elicit more information from social media users? What is their background?
"Sinn Féin must also answer who developed the database and reveal how the party paid for this system."
