Fianna Fáil has strongly criticised British Prime Minister Theresa May after it emerged that her powerful Brexit cabinet committee has no permanent slot for the Secretary of State for Northern Ireland, James Brokenshire.
Mr Brokenshire will instead attend meetings of the committee, which is mapping out Britain's exit from the European Union, at the request of Ms May.
Several senior Tory politicians who campaigned for Brexit have, in contrast, been handed permanent slots.
These include the British Foreign Secretary Boris Johnson and Secretary of State for exiting the EU David Davis.
Mr Davis was recently in Dublin to discuss the prospect of changes to the border as a result of Brexit.
However, it has emerged that the secretaries of state for Northern Ireland, Scotland and Wales do not have permanent attendance.
Instead, they will attend meetings of the European Union Exit and Trade Committee "as required".
Fianna Fáil last night hit out at the revelation that Mr Brokenshire is not one of the 12 permanent members.
The party's foreign affairs spokesperson Darragh O'Brien described the decision as a "new departure" and said the Government must now register its concern.
"This is a deeply worrying development and further proof that Northern Ireland is not a priority for the Tory Government," Mr O'Brien told the Irish Independent.
"It's a new departure quite frankly and we will be raising our concerns in the strongest possible terms with the British government because it's clear Northern Ireland is not on their radar."
Mr O'Brien also hit out at claims that the Budget announced last week is 'Brexit proof'.
"Quite clearly it's not and it reinforces our point that the Government here needs to step up to the plate."
The Dublin Fingal TD said he met last week the British Ambassador to Ireland Robin Barnet to discuss his party's concerns in relation to the border.
Questions over the North-South border have been rampant since the UK voted to leave the European Union, with fears that border controls would have to be put in place to control immigration.
Such measures could be seen as a violation of the Good Friday Agreement.
But it emerged last week that Britain is hoping to move frontline immigration controls to Irish ports and airports to avoid enforcing a 'hard border' between Northern Ireland and the Republic.
The proposed measures would be mainly aimed at non-Europeans wishing to enter the common travel area between Ireland and Britain.
The UK House of Lord Committee looking at the implications of Brexit on Irish and UK relations will hold hearings today and tomorrow in Dublin and Belfast.
Among the witnesses to give evidence at Stormont today will be SDLP leader Colum Eastwood and Ulster Unionist leader Mike Nesbitt, as well as academics, representatives from InterTrade Ireland and the Confederation of British Industry.
In Dublin tomorrow, evidence will be given by Edgar Morgenroth from the ESRI and Richard Pym from AIB, as well as representatives from IBEC and ICTU.
Government officials are also preparing for the all-island Brexit forum due to begin its work next month.
The forum is due to be chaired by Taoiseach Enda Kenny. However, Northern Ireland First Minister and DUP leader Arlene Foster has said she will not be attending.
Ms Foster said when the forum was first raised in July, it was handled badly.