It is also deploying machine learning to identify inappropriate content. "Our goal is simple: to help ensure a free, fair and transparent vote on this important issue."
The referendum will decide the fate of the Eighth Amendment to the Irish Constitution, one of the most severe prohibitions on abortion in the Western world.
Approved by Irish voters in 1983, the law gives the mother and the unborn an equal right to life and proscribes termination even in cases of rape, incest and fatal fetal abnormality.
Debate over the Eighth has bitterly divided the Irish public; opinion polls suggest a slight majority for repeal. But it has also drawn the attention of international interest groups, lent a megaphone by social media as the influence of the Catholic Church has waned.
While Ireland forbids foreign spending in campaigns, and prohibits political advertising on television and radio altogether, its election law is virtually silent on digital activity.
As a result, individuals and groups from outside of Ireland - primarily from the United States, Britain and Canada - have been waging an online campaign to influence the vote, according to the Transparent Referendum Initiative, a nonpartisan organisation tracking paid online advertising.
Foreign efforts, still dwarfed by domestic activity, have mainly opposed repeal, the initiative's records show.
Craig Dwyer, one of the initiative's founders, said there had been an increase of 150 advertisements over the past week alone, including domestic and foreign messaging. "The million-dollar question," Dwyer said, "is how much money has been spent on these advertisements."
A Facebook spokeswoman said the company would not release that information. She also declined to offer any information about the foreign entities seeking to place referendum-related advertisements.
Data compiled by the initiative, which depends on crowdsourcing from users, reveals that numerous American-based groups have penetrated the online debate in Ireland.
Advertisements have appeared from Live Action, a group led by anti-choice activist Lila Rose best known for hidden-camera videos of Planned Parenthood clinics; Radiance Foundation, a Virginia-based anti-abortion group that has drawn criticism for using the mantra of the Black Lives Matter movement to shame women for ending their pregnancies; and Expectant Mother Care/E.M.C. Frontline Pregnancy Centers, a group that carries out anti-abortion activity in New York City, which it has labelled the "abortion capital."
A post from Expectant Mother Care that appeared to target users in Ireland warned of "an existential threat" to the Irish unborn and shared a video from Save the 8th, the main campaign group urging preservation of the restrictive amendment.
Save the 8th has retained the services of Kanto, a London-based data firm and political consultancy tied to the Brexit campaign to take the United Kingdom out of the European Union in 2016.
Kanto's director, Thomas Borwick, previously worked for Cambridge Analytica, the firm hired by Donald Trump's presidential campaign and recently accused of misusing the data of 50 million Facebook users. Borwick said he could not comment on ongoing campaigns.
James Lawless, an Irish deputy who has been a leading voice for digital campaign regulation, said the Irish case is significant because it reveals that the problem is not limited to Russian agression but rather present in any high-stakes contest in which foreign actors can take advantage of pre-Internet election law.
"How we communicate has changed hugely," Lawless said. "But there's a total vacuum in regulation in the online space."
