The Labour party leader said the refusal of Sinn Féin to add to the numbers opposing a 'no-deal' Brexit in Westminster remains infuriating.
Brendan Howlin is welcoming Jeremy Corbyn's initiative to hold a no-confidence vote in the British government and become a 'temporary' prime minister in order to prevent a crash-out Brexit
However, he said if ever Sinn Fein wanted to prove its credibility as a party prepared to put Ireland first, north and south, this is it.
He said from an Irish perspective, it is clear that Westminster is on a knife-edge.
"It is infuriating that this vote may well be lost by one or two votes because the majority enjoyed by Johnson in the British parliament is a majority of one," he said.
"Every single vote will be pivotal. If Sinn Féin could provide seven additional no-confidence votes, I would ask them to do that, on this once-off issue that is historically important for the people on the island of Ireland."