FACEBOOK and Google took steps to prevent foreign involvement ahead of Ireland’s vote on abortion last month.

On May 8, Facebook started to block ads related to the referendum that didn’t originate from advertisers in Ireland.

A day later, Google announced it would suspend all ads related to the referendum. They were blocked until Irish voters went to the polls on May 25.

Ireland voted overwhelmingly to overturn the abortion ban by 66.4 per cent to 33.6 per cent.

Both sides spent heavily on online advertising, capitalising on the power of social media advertising to directly target voters without the message being mediated by traditional news outlets.

However, the referendum prompted Facebook and Google – both of which have large workforces in Dublin – to keep a close eye on online campaigns.

The bans prevented paid messages relating to the referendum from appearing on its services, which dominate many aspects of online advertising.

In April, Irish data protection commissioner Helen Dixon had said it was possible that foreign organisations could try to sway the referendum.

Ireland's electoral laws ban foreign organisations from funding campaign groups in the country.

However, social media sites and search engines are not prohibited from carrying foreign-funded advertisements.

There has been mounting pressure on social media companies for greater transparency, following revelations over who is behind political advertising campaigns and how they target the public.

Claims that Cambridge Analytica used data gathered from millions of Facebook profiles, and that Russia-backed advertising influenced the US presidential election, have led to fears that political campaigning on social media could be a threat to democracy.

In Ireland, there were complaints from local groups that foreign campaigners with big budgets were trying to sway the vote.