Fine Gael has instructed its 246 councillors around the country to block the nomination of potential independent presidential candidates.
An order from party headquarters, seen by RTÉ News, has been sent to all 31 Fine Gael council groups setting out the position.
The instruction says that "as Fine Gael has a candidate in the Presidential Election, Fine Gael public representatives are only to nominate the Fine Gael candidate.
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"Fine Gael public representatives cannot in any way facilitate the nomination of any candidate other than the ratified Fine Gael candidate."
It continues: "In the event of a vote at any local authority on the nomination of a person other than the ratified Fine Gael candidate, the Fine Gael local authority members are whipped to oppose that nomination."
The diktat comes as special council meetings kick off on Monday to consider applications from aspiring presidential candidates.
At least 20 of the 31 councils will hold such meetings to hear from candidates. Individuals require the backing of four local authorities to get on the ballot paper
Under the Constitution, candidates seeking to contest the presidency must secure the support of either 20 Oireachtas members or four local authorities.
For independents, council nominations have historically been a key path to the ballot paper - a path now threatened by party-political interference.
Gareth Sheridan, Nick Delehanty, Maria Steen and Conor McGregor are among the many applicants who have approached councils for their backing.
Minister for Finance Jack Chambers has said that Fianna Fáil will decide next week on a formal position for its councillors on nominating independents for the Presidential Election.
Asked about Fine Gael's diktat to councillors instructing them to block independents, Mr Chambers said that Fianna Fáil is currently in a selection process for its own candidate.
However, after that process is concluded on Tuesday, Fianna Fáil's National Executive will meet later next week to decide on a formal position of councillors.
He added that he expected that in the interim, most of the party's councillors would get behind their own candidate.
Aontú leader Peadar Tóibín criticised the party's decision. In a post on X, he said: "FG is shutting down councils from democratically selecting an alternative candidate for the presidential election."
Independent Meath councillor Joe Bonner has also strongly criticised the directive issued by Fine Gael leadership.
Calling the move "a blight on democracy," Cllr Bonner condemned what he sees as a top-down attempt to control the nomination process and silence legitimate voices before they can even make their case to the public.
"This directive denies councillors their democratic right to vote according to conscience," he said.
"And more importantly, it denies the public their right to hear from all eligible candidates - not just those sanctioned by political parties."
Meanwhile, Independent Ireland leader Michael Collins described the decision to ban Fine Gael councillors from supporting independent candidates in the upcoming Presidential Election as an "unprecedented threat to democracy".
Deputy Collins said the move exposes the hypocrisy of establishment parties who constantly speak about "protecting democracy" while in practice working to shut down alternative voices.
"For all the talk from Fianna Fáil and Fine Gael of threats to democracy from disinformation and so-called hate speech, the real threat comes from within - from an establishment elite that refuses to allow the Irish people a fair choice," he said.
"Simon Harris's diktat to Fine Gael councillors is nothing short of a gag order," he added.
"It shows a fear of competition, a fear of debate, and a fear of allowing the public to have their say on the messes these parties have made. It is an insult not just to independents but to the democratic rights of voters across the country."
