The Data Protection Commission (DPC) has contacted Sinn Féin over its collection of data from Facebook to target voters for engagement, including a doorstep canvass.
It emerged last weekend that the party had asked officials working for it to use personal information posted on people's Facebook pages to identify where they live.
Thereported that people attending an internal digital training seminar were told "Facebook is king".
They were also urged to cross-reference data taken from Facebook profiles with Sinn Féin's own searchable digital electoral register database, Abú.
The digital media training presentation last September outlined the benefits of the social media platform, including through targeted advertising.
Sinn Féin said it complied fully with Facebook's terms of service and all relevant regulations, but now it has emerged that the DPC has sought more information from the party about its use of the data.
Deputy commissioner Graham Doyle confirmed the DPC had put a series of questions to Sinn Féin and was awaiting a response.
It is understood the DPC wrote to the party on Wednesday over how it was targeting people on Facebook and it is believed the DPC is concerned about transparency and the collation of more data than the party would need.
It will also examine whether the party's actions comply with data protection legislation and GDPR requirements.
A Sinn Féin spokesman said the party would engage with the DPC.
"We can confirm that we have received correspondence from the Office of the Data Protection Commissioner," the party spokesman said. "We look forward to engaging with them.”
Last month, Sinn Féin confirmed that supporters based in Serbia and Germany were involved in managing the party’s social media channels.
At the time, the party said: "Sinn Féin advertising on Facebook is managed in Ireland in full compliance with Facebook's advertising policies.
"A party supporter who is now based in Germany works for our social media team. In Serbia, we have two party supporters who occasionally help out our social media team. This information is publicly listed on Facebook."
It labelled as "spin" Fine Gael queries about the practice, but Fine Gael senator John Cummins said there were questions that needed to be answered.
"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?"