A Fianna Fáil senator has called for greater clarity about who would be entitled to vote in a border poll.
Senator Mark Daly has make the comments following an analysis of court documents following a Northern Ireland High Court judgment and papers submitted by then northern secretary, Karen Bradley.
Under the Good Friday Agreement and the Northern Ireland Act, the Secretary of State for Northern Ireland has the power to call a referendum, but also has the power to decide who gets to vote in that referendum, Mr Daly said.
His comments follow the publication of a poll by LucidTalk, a Belfast research company, based on responses from 2,386 people which was conducted last week in Northern Ireland and published in the Sunday Times.
The poll, which has margin of error of 2.6%, found that two out of three voters believed Brexit made it more likely that the Northern Ireland would join with the Republic.
Senator Daly said that currently in a UK referendum, only British, Irish and Commonwealth citizens aged 18 or over on polling day are entitled to vote.
However, in the Scottish Independence referendum, those entitled to vote also included EU citizens and those aged 16 and over.
Senator Daly said the Secretary for State can decide who votes in a referendum but has yet to make clear who would be entitled to vote.
"As it stands, a referendum on a United Ireland could potentially be decided by the Secretary of State before a single vote is cast," he said.
He added: "The major lesson for Ireland from the Brexit crisis is the unforeseen consequences of holding a referendum with proper planning.
"A United Ireland requires long-term planning and preparation with all sides."