At least a quarter of meetings of the North-South Ministerial Council that were due to take place last year did not go ahead because of a DUP boycott.
They included sectoral meetings to discuss cross-Border co-operation on agriculture, the environment and languages.
No meetings are currently scheduled for this year, but the DUP's position is not expected to change unless amendments are made to the post-Brexit Northern Ireland protocol.
It is not yet clear what the consequences of this might be, but Deputy First Minister Michelle O’Neill previously told the Assembly it could impact on the delivery of “crucial key projects”, particularly in regard to infrastructure.
She also said the Irish Government’s increased investment in the Shared Island Fund was “in jeopardy because of political posturing and electioneering by one particular party”.
However, a potential threat to €1 billion of EU Peace Plus funding – which required council sign-off – was averted due to a workaround which saw it approved at a health meeting in October, potentially setting a precedent that could be used to avert similar problems in the future.
The council was established as part of the Belfast Agreement to "develop consultation, co-operation and action within the island of Ireland". Meetings had resumed in autumn 2020 following the restoration of the North's powersharing institutions that January after a three-year absence.
In total, one plenary and eight sectoral meetings of the council – covering health and food safety, education, transport, trade and business development and inland waterways – went ahead last year.
Meetings can only proceed with the participation of both a unionist and a nationalist minister from the North, and can only be formally scheduled once there is cross-community agreement on the agenda.
DUP leader Jeffrey Donaldson announced in September that his party would no longer take part in such meetings. He said that while the present protocol arrangements remained in place "it cannot be business as usual for North-South relations". The DUP would immediately withdraw from the structures of the Belfast Agreement relating to North-South co-operation, with the exception of "important health-related matters", he said.
The unionist parties in Northern Ireland are opposed to the protocol, which aimed to avoid a hard border on the island of Ireland by placing a customs and regulatory border in the Irish Sea. They argue it has created economic difficulties for the North and undermined its constitutional status as part of the UK.
Negotiations to resolve the issues around the protocol are ongoing between the UK and the EU.
Following legal action by Belfast businessman Sean Napier, a High Court judge ruled that the DUP boycott was "unlawful" and in breach of the pledge of office taken by Executive ministers as part of the ministerial code.
In a subsequent judgment, Mr Justice Scoffield said the ministers who were boycotting the meetings were in "abject breach of their solemn pledge" but declined to make any order mandating them to set a date and agenda for the next council meeting.