The North's First Minister says there is far too little co-operation between North and South as the six counties began two more weeks of lockdown.
Arlene Foster says it is "regrettable" the Tánaiste even suggested a ban on cross-border travel for Christmas.
Last weekend, the four UK jurisdictions agreed to try and align their Christmas lockdown plans and allow travel between them.
Ms Foster told reporters at a press conference last night they are hoping to include the Republic in that too.
"It appears that the border has made a reappearance again after Northern Ireland being lectured for four years in the context of the European Union negotiations that the border was completely open," said Ms Foster.
"He has to explain why that is the case. I think it is really regrettable.
"What we want to see is good cooperation across the whole of the British Isles so that families can be together."
Sinn Féin's Michelle O'Neill says the Tánaiste is speaking from a position of ignorance.
Ms O'Neill said Mr Varadkar has proved that he is completely out of touch with the reality of life.
"I think his comments reflect that. I think that we can do more and we can be more joined up.
"It's important that we are. We said this the whole way through the pandemic, we have a memorandum of understanding across the island.
"Certainly, I would like to see a lot more communication as well. I think communication can always be improved and needs to be improved."