Gardaí have said it was "not appropriate" for a Garda to appear in a photocall organised by the Yes Equality campaign.

It comes after a uniformed Garda and retired judge, Catherine McGuinness, were pictured with an enlarged voter registration form outside Pearse Street garda station yesterday.

"While the event was held in good faith [..] it was not appropriate" given Garda status as "apolitical and impartial" pic.twitter.com/IcjhvngatS — Gavan Reilly (@gavreilly) April 20, 2015

Yes Equality are running a voter registration campaign to encourage people to register by May 5, in time to vote in the Marriage Equality referendum on May 22.

Gardaí released a statement saying: "In relation to yesterday’s photocall at Pearse Street Garda Station in Dublin, while the event was held in good faith to promote the fact that people can register at Garda stations to vote in the upcoming referenda, it was not appropriate for this kind of photocall to take place given An Garda Siochana’s status as an apolitical and impartial organisation."

It is not clear if the invesigation was started because of a complaint, but a Garda press office spokesman said: “the matter is being looked into.”

A campaign advocating a no vote in the referendum, Mothers and Fathers Matter said it was a “sinister development”.

Campaign spokesman Keith Mills said: "We have not had the politicising of the gardaí since the foundation of the State and we shouldn’t have it now just because there is a political consensus among the elite in Ireland about this issue."