There have been proposals to change the rules of succession
Catholics do not owe any political allegiance to the Vatican, the SDLP's deputy leader has said.
Alasdair McDonnell made the comment after the DUP's Jeffrey Donaldson said he opposed changing the rules of royal succession in the UK.
Mr Donaldson said a potential monarch who was Catholic would owe their "first allegiance" to the Vatican.
However, Mr McDonnell said Irish Catholics get their "religion from Rome but their politics from Ireland".
The comments followed discussions between Gordon Brown and Buckingham Palace on plans to change the rules of succession to the throne, including giving royal women equal rights and the ban on heirs to the throne marrying Catholics.
A Private Members' Bill aimed at ending the discrimination had its second reading in the House of Commons on Friday morning but the government is not backing it.
The rules of succession are laid down in the 1701 Act of Settlement.
It states heirs to the throne lose their right to be the sovereign if they marry a Catholic or convert.
In addition, male heirs are given precedence.
Mr Donaldson, a junior minister in the Stormont Executive, said that there were constitutional issues to changing it.
"A potential monarch who is a Roman Catholic, a member of that church is required to owe their first allegiance to the Vatican," he said.
"Now the Vatican is a state, it is a constitutional entity it is recognised as a state in international law there is, therefore, a potential conflict of interest between being the head of state of our own country and owing allegiance to another state."
He added that 15 other countries which had the Queen as their head of state would also need to change their constitutions.
Mr McDonnell said Mr Donaldson was wrong to say Catholics owe any temporal or political allegiance to the Papacy or the Vatican State.
He said Irish republicans have no interest "in the succession to the British throne or any other throne".
"Daniel O'Connell nailed the lie during the struggle for Catholic emancipation when he made it clear that Irish Catholics might take their religion from Rome but they got their politics from Ireland," he said.
"It is astounding and quite alarming that a junior minister should so deeply misunderstand and misrepresent more than half a million of his close neighbours."
If the Act was changed to give royal daughters equal rights, Princess Anne would become fourth in line, behind Prince Harry. Currently she comes after the Duke of York and the Earl of Wessex, and their children.
As things stand, Prince William cannot marry a Catholic and become king.
And if he has a daughter she cannot be queen if she has a younger brother.
Prince Michael of Kent, the Queen's first cousin, is among a small number of royals who have renounced their place in the line of succession by marrying a Catholic.
The reform bill has been introduced by Liberal Democrat MP Evan Harris.
His bill would not change the law preventing a Catholic from being the monarch.