The body representing Irish SMEs has sharply criticised the UK's threat to trigger Article 16 of the Northern Ireland Protocol, potentially over the role of the European Court of Justice (ECJ).
In a letter to the British ambassador to Ireland Paul Johnston, seen by RTÉ News, ISME's chief executive Neil McDonnell said that since the signing of the protocol, the organisation "has not heard the ECJ issue raised from a single one of our cross-border members. Nor in our contacts with other trade representatives in Northern Ireland has this issue been raised."
Mr McDonnell added: "If Northern Ireland is to retain access to the single market, that must entail oversight of a fair and competitive market in that jurisdiction by the ECJ. We believe most Northern Ireland citizens and business owners see advantage in and accept this position."
There are growing expectations in Dublin and Brussels that the UK intends to trigger Article 16 in the coming weeks.
The letter said that allowing Northern Ireland to continue operating within the EU's single market was "a significant concession" and addressed the key desire to avoid a border on the island.
"Remaining within the single market must logically require the retention of the ECJ in order to resolve intra-single market disputes that will inevitably arise, as they do today between EU member states," Mr McDonnell wrote.
He also suggested that as a former chief executive of the Scotch Whisky Association, the British Brexit minister Lord Frost, who has repeatedly threatened to trigger Article 16, would have supported ECJ decisions which protected both Scotch and Irish distillers from discriminatory barriers to trade that France had attempted to raise.
"It is very difficult for us to accept the bona fides of HM Government in general and Lord Frost in particular on the issue of the ECJ as it pertains to Northern Ireland...
"Lord Frost publicly indicated his support for maintenance of the single market in this regard in early June 2016," the letter states.
Mr McDonnell concluded that the triggering of Article 16 would undermine the EU-UK Trade and Cooperation Agreement.
"This would of course have serious implications not just for an even greater reduction in the wealth of the United Kingdom, but for tens of thousands of businesses across the island of Ireland and Great Britain," the letter stated.
ISME has some 10,500 members nationwide.
A British Embassy spokesperson said: "We are seeking a consensual solution that protects the Belfast (Good Friday) Agreement and the everyday lives of people and businesses in Northern Ireland.
"Our proposals would reduce disruption for businesses, particularly SMEs, and protect the Belfast (Good Friday) Agreement."
Tánaiste Leo Varadkar has said that he hopes the British government will listen to the opinion of the business community and people in Northern Ireland who broadly support the implementation of the Northern Ireland Protocol.
Mr Vardakar said he did not want to see the EU suspend the trade agreement with the UK and he "really hopes Britain does not go do this road".
He said this could "potentially undo" Brexit and is not good for Ireland, north or south, and that no preferable alternative has been put forward.
The minister said that invoking Article 16 does not set aside the protocol, which he said is working to prevent a hard border and to strengthen the all-island economy and protect the single market.
He said the disruption it has caused to trade between Northern Ireland and Britain has been addressed by the European Commission, but that this is not accepted by the British government.
He said that triggering Article 16 of the protocol would allow Britain to take unilateral measures in a time-limited and proportionate way but does not mean "deleting or abandoning" it.
He said "that's not the case".