An Irish fishing boat was blocked from entering waters around Rockall in the North Atlantic by a Scottish patrol vessel.
The Donegal-based Northern Celt was stopped by a Marine Scotland boat on Monday.
Its captain, Adrian McClenaghan, told Irish broadcaster RTE that his crew could no longer fish within 12 nautical miles of the eroded volcano as a result of Brexit.
The Irish Department of Foreign Affairs said it was aware of the incident.
A spokesperson said: “We are aware of contact between an Irish fishing vessel and a Marine Scotland patrol vessel on January 4.
“We are in contact with the Scottish and the UK authorities on this.”
The Scottish Government later said the Irish vessel had breached its licence conditions and had been reported.
Rockall is situated around 160 nautical miles west of Scotland’s St Kilda and around 230 nautical miles north-west of Ireland’s Donegal coast.
The uninhabitable rock has been a cause of contention for a number of years, with the UK stating it is part of its territory – a claim which the Irish government refuses to recognise.
The UK claimed Rockall in 1955 and incorporated it as a part of Scotland in 1972.
A row erupted in June 2019 when Scotland threatened action if Irish vessels continued to operate in the zone around Rockall.
At the time the Scottish Government said it was defending the interests of its fisheries against “illegal activity” around the granite islet.
In response to Monday’s incident, a Scottish Government spokesperson said: “On Monday, Marine Scotland carried out a routine inspection of a vessel outside of territorial waters around Rockall.
“The vessel was suspected of fishing in Scotland’s marine areas without the right to do so and in breach of its licence conditions.
“Marine Scotland is responsible for the monitoring and enforcement of marine and fishing laws relating to Scotland’s marine areas. It regularly monitors the seas around Rockall.
“As per long-standing arrangements, Marine Scotland has reported the breach of licence conditions to their Irish and UK counterparts.
“We will always engage constructively with our EU partners and ensuring the sustainable management of fish stocks is at the heart of our partnership working.”