The federal Green party will vote against a Conservative motion to form a committee to investigate Liberal spending on COVID-19.
The three Green votes would all but assure defeat of the Tory motion.
The Liberals said the motion meant the Trudeau government had lost the confidence of Parliament.
When a government loses a confidence vote, an election quickly ensues.
The Bloc Quebecois earlier indicated its members would back the Tories.
NDP Leader Jagmeet Singh would not say if his party will vote with the Liberals.
But he did say he would not allow the Liberals to be able to hold an election.