Fianna Fáil leader Micheál Martin accused the Taoiseach of making "asinine'' remarks on Brexit during sharp Dáil exchanges.
"It does him no justice in terms of seriousness,'' said Mr Martin.
Leo Varadkar had said on Tuesday he read a report that last weekend's Fianna Fáil's ardfheis had passed a motion calling for an electronic border with gantries and M50-style tolls.
Mr Martin said the Taoiseach knew full well what his position as Fianna Fáil leader was on Brexit.
Mr Varadkar said there were also reported comments that Fianna Fáil would prepare for a hard Brexit.
“How else would it prepare for a hard Brexit other than by going around the place scoping out sites for customs posts and truck stops and training border guards and dogs ?’’ he added.
Mr Varadkar warned about “self-fulfilling prophecies”, which an electronic border might become if it was proposed.
