DUP MP Jeffrey Donaldson has accused Taoiseach Leo Varadkar of "poor manners" for visiting Northern Ireland today "outside of normal protocol".
The Irish PM met with the EU's Chief Brexit Negotiator Michael Barnier this morning for an All Island Dialogue conference in Dundalk, before crossing the border into the North.
Among Mr Varadkar's engagements there this afternoon are visits to Warrenpoint Harbour and an integrated school in Loughbrickland, Co. Down.
But Mr Donaldson, the MP for Lagan Valley, has slammed the Irish PM's decision to visit Northern Ireland without informing any "local representative".
In a statement, Sir Jeffrey said: "Leo Varadkar's visit is another demonstration of the poor manners and disrespect which appears to be the Irish government's Brexit strategy.
"Having told unionists just over a month ago that he recognised statements and actions by the Irish government were unhelpful or intrusive, he follows this up with a visit which no local representative is informed about and none of the other normal protocol is followed."
David Davis was forced to apologised last week after failing to inform Northern Irish politicians about his first visit to the Irish border as Brexit secretary.
Speaking at the All Island Dialogue conference earlier, Mr Varadkar said he had "no interest in a land grab" in the North - but Donaldson went on to accuse the Taoiseach of using Brexit to "undermine" Northern Irish politics.
Sir Jeffrey added: "It is increasingly apparent that the Irish government does not seem to care about securing a sensible and pragmatic outcome from Brexit which can work for both Northern Ireland and the Republic.
"Their preferred approach is to use Brexit in whatever way possible to undermine Northern Ireland and particularly its constitutional position.
"Whilst Mr Varadkar may say that he wants to find solutions to the issues facing us there is little demonstration of him working constructively to find them."