CFMEU Mining and Energy Division Victorian Branch secretary Geoff Dyke said the state is destined to experience blackouts this summer, claiming the Valley's ageing power stations will not be able to handle the heat.
"I don't think we might have blackouts I guarantee that we will," Mr Dyke said.
He also said the region would need to transition to nuclear power to keep up with growing demand for electricity as the Valley prepares to move away from coal-fired power.
Mr Dyke said the planned closure of power stations in the region would lead to statewide blackouts, which he said would likely become a regular occurrence.
"We'll have a really newsworthy one the way we're going, it's just luck that's been saving us," he said.
"The state is quite vulnerable and if Victoria blacks out we will have no power for a couple of days.
"Restarting a grid you have to balance generation and load, you can't just switch it back on, it takes time."
Mr Dyke also said the power stations were already struggling to keep up with increasing demand for electricity ahead of the peak-demand summer season.
"What I do know? And I've said it over and over again, we will have blackouts because we haven't got enough electricity, we haven't got enough dispatchable power," he told The Express.
"It will come to a crunch [and] we've had blackouts this summer just gone and we had a pretty mild summer.
"If we get a decent summer Yallourn [Power Station] is that unreliable it's not going to be able to stay on if we have four weeks of hot weather."
Head of Yallourn Mark Pearson admitted "an older power station like Yallourn has its limits", but said it would "continue to play its vital role in generating electricity for Australia".
"But there is no doubt that at certain times Australia's energy demands are higher than the network can reliably deliver," Mr Pearson said.