The Yallourn power station in eastern Victoria could remain closed for several days after a fire forced the plant offline.

The station supplies a quarter of Victoria's energy and yesterday's blaze shut down its operating units.

The fire comes amid union plans to step up industrial action at the site over a pay dispute.

Energy Australia had locked CFMEU members out of the power station.

George Svigos from Energy Australia says it is investigating the cause of the fire and assessing what needs to be done to fix the generators and get the station back online.

"These are highly complex machines and we need to make sure we've got the right plans in place to do this safely and securely," he said.

"We're really at that stage now of scoping that work."

The CFMEU's Luke Van Der Meulen says the timing of the fire and the escalating industrial action is coincidental.

He says union members will meet on Monday to discuss their next step.

"Our aim is to negotiate an agreement with the company and get on with our lives, have our members back at work and have an agreement in place," he said.

"That'll continue to be our goal."