Hassan Yussuff is warning the prime minister he will face the wrath of the labour movement if it feels forced to push back against Conservative policy.
Yussuff tells The Canadian Press the union movement will do everything it can to ensure the Conservatives are not re-elected next year.
But he is also offering to work collaboratively with any government.
The 57-year-old Yussuff defeated the long-serving Ken Georgetti in a vote at a convention in Montreal on Thursday.
He is promising to be more engaged and aggressive than Georgetti, who had been president since 1999.
The labour organization said Yussuff was the first person of colour to be elected to an executive position when he became executive vice-president in 1999.
Yussuff was born in Guyana, South America, and settled in Toronto when he came to Canada in 1974.
The Canadian Labour Congress, which represents 3.3 million workers, brings together national and international unions as well as provincial and territorial federations of labour and 111 district labour councils.