The group claims the Gentilly-2 power plant constitutes a key element in the province's energy safety. It also said it was surprised by Hydro-Québec's recommendations to shut down the nuclear plant.
The union represents about half of the 700 workers at Gentilly-2.
In a report sent to French paper Le Devoir, province-owned Hydro-Québec concludes the revival of Gentilly-2 is not justified in the financial plan.
The report states the cost to reboot the plant would cost $2.4 billion in 2008. The price of electricity created would then cost 9.7 cents for every kilowatt per hour. This is in comparison to the 6.2 cents expected for the La Romaine central being built in northern Quebec.
Union president Richard Perreault said Quebec should refrain from putting "all of its eggs in the same basket" and only opt for hydroelectric power.
He also added that Gentilly-2 offers well-paid salaries to people of the Mauricie region of Quebec.
The company expects a $215 million deficit by 2017. This means every job at the central would cost nearly $250,000 to maintain.
Perreault said new power-generating technologies like wind turbines would not represent effective investments based on their lower performances.
The Parti Québécois supports the closure of the Gentilly-2 nuclear plant but the government's opinion is facing strong opposition in the Mauricie and in Central Quebec.
Perreault said the PQ's decision to close the plant is a bold move to make shortly after being elected and that it is irresponsible for the region's economic development.
Workers at the plant have received notice saying Hydro-Québec would proceed with the closure.