President Michael D Higgins will have to fight an election if he wants a second term, as Sinn Fein is preparing to nominate a candidate.
Party chiefs will meet in 10 days' time to decide on their strategy but leader Mary Lou McDonald has given a clear indication that they will force a contest.
She said that while Mr Higgins is "a fine individual personally and politically", he should not be allowed to occupy the highest office in the country without an electoral mandate.
"I don't think it's appropriate that the incumbent simply rolls into another term of office seamlessly," she said.
Among the party names understood to be in the mix are outgoing Cavan/Monaghan TD Caoimhghin O Caolain and MEP for Ireland South Liadh Ni Riada.
Senator Frances Black has also been suggested as an Independent candidate who the party could help to get a nomination. Sinn Fein votes helped the well-known singer win her Seanad seat in 2016.
Ms Black's name has been circulating among Sinn Fein's TDs - but she is understood to have told Seanad colleagues she is not enthused by the idea of running against Mr Higgins.
The President is expected to formally announce in the coming days that he wants another seven years in office.
Fianna Fail and a raft of Government ministers have already given him their full backing.
Taoiseach Leo Varadkar is refraining from announcing Fine Gael's stance until after Mr Higgins outlines his intentions.
However, senior party sources say the Taoiseach is certain to back Mr Higgins. The party spent €4.65 on every vote cast for its 2011 candidate Gay Mitchell.
Ms McDonald said: "If Fianna Fail and Fine Gael don't want an election - if they believe the first citizen should not have a democratic mandate that I believe they should have, or in the case of President Higgins a renewed mandate if that's what he seeks - then I beg to differ with them."
Asked whether cost would impact on Sinn Fein's decision, Ms McDonald acknowledged that it would be "an expensive campaign" .
However, she added: "I actually think that the presidential campaign is unique. It affords in a fairly non-adversarial atmosphere an opportunity to debate and to discuss matters. I think we should avail of that.
"It's about the country, it's about direction, it's about big, big politics."