The Fianna Fáil organisation in Mayo has issued a warning to party members intending to canvass for Independent deputy Beverley Flynn in the general election.
A directive was circulated to cumann secretaries by the party's Dáil ceantair informing them that such action would result in automatic expulsion.
Éamon Joyce, secretary, explained that a resolution was unanimously passed at the recent ardfheis altering Rule Seven of the party's constitution.
The amendment reads: "Any member of Fianna Fáil who actively supports a candidate other than a duly-ratified party candidate at local, Dáil or European Parliament elections shall automatically be deemed to be expelled from the organisation, subject to the right of an appeal to the ardchomhairle."
A Fianna Fáil spokeswoman said: "There is a rule of the party that members must support their party candidates, and Mayo would be no exception to that." As for the threat of expulsion, she said: "That's the party rule as passed democratically by the party."
The move follows speculation within the party in Mayo that Ms Flynn would "not be obstructed" in her re-election bid. The Castlebar TD was expelled from Fianna Fáil in May 2004 following her failed Supreme Court libel appeal against RTÉ.
Claims that she will be reinstated to the party if she retains her seat were emphatically denied by Mr Joyce.