The future of Canadian Prime Minister Justin Trudeau’s leadership is increasingly uncertain after New Democratic Party (NDP) leader Jagmeet Singh, a key ally, said he would introduce a motion to topple the minority Liberal government.

Singh, whose party has been helping keep Trudeau in office, announced in an open letter posted on social media that he would declare a loss of confidence in the Trudeau-led Liberal government next year, a move that would trigger an early election if other opposition parties support his move. Canada’s next election must be held on or before October.