Hydro Tasmania employees who face redundancy have until Monday to decide whether they will leave the organisation or take a lower paid position within the organisation, the union says.
The state-owned company on Wednesday announced it would shed 50 positions as it restructured its business.
It said while new positions would be created as it adapted to the changing national energy market, other roles would become redundant.
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Karen Tantari, of the Australian Services Union, said the union was aware they were looking at a business restructure, but it was not briefed or consulted about redundancies.
She said that would now happen on Friday morning.
"Members were going into meetings in 15-minute intervals and told they were going to be redundant as their position was displaced," she said.
"They were told they could take a redundancy or take a lower graded position.
"And they've got until Monday to provide feedback.
Ms Tantari said contract administrator, service desk operator, payroll, finance, and procurement positions were some of the roles to face the axe.
Energy Minister Guy Barnett on Thursday said the government supported consultation with its workforce.
"That is a matter for Hydro Tasmania, obviously it is a matter for the board, the CEO to ensure they consult with the workforce and I would encourage both management and Hydro Tasmania to consult very closely with their workforce," he said.
"Hydro needs to be fit for purpose as the national electricity market transitions to a new arrangement where there is a move away from coal towards renewable energy.
"They will be employing some new people to ensure they are fit for purpose and transitioning through that process.
"They need to be efficient; they need to keep downward pressure on prices."
Labor's energy spokesman David O'Byrne said Mr Barnett had failed to stand up for the workers set to lose their jobs.
"It's just not good enough that Mr Barnett has washed his hands of this serious matter saying the job losses are a matter for the business and its board when they are certainly a matter for him," he said.
"It's not good enough that Guy Barnett promised to protect jobs - not axe workers - and then is complicit in getting rid of five per cent of the Hydro workforce."
Hydro Tasmania recorded a $154 million profit in 2019-20 which was 54-per-cent above its forecast.
Company chief executive Evangelista Albertini was appointed to the top job just six months ago after Steve Davy left the position.