The Opal Australian Paper mill at Maryvale in the Latrobe Valley is due to run out of materials to make white paper about December 23.
Its supplier, government-owned timber business VicForests, has been ordered to scale back harvesting in parts of East Gippsland and the Central Highlands, where two endangered possum species live.
The mill anticipates some workers will be temporarily stood down, while others may have a reduced workload.
Australian Manufacturing Workers Union organiser Stephen Dodd expects about 250 people may initially be affected.
"They're very worried," Mr Dodd told AAP.
"Obviously, everybody's worried out there about the impact that could have on them personally and also on the region."
The paper mill is one of the biggest employers in the Latrobe Valley and jobs are considered to be well paid, prompting fears there could be a flow-on effect in surrounding towns.
The area is still coming to terms with the closure of major employers, including the Hazelwood power station, which shut in 2017.
Mr Dodd represents about 100 workers, while others are represented by the Electrical Trades Union and the Construction, Forestry, Maritime, Mining and Energy Union.
AAP has sought comment from both unions.
A spokesperson for Opal Australian Paper said in the long term the company is considering scaling down white-paper operations or stopping them entirely, which could lead to potential redundancies.
"This is a complex and ever-changing situation and no longer-term decisions on operational changes have been made at this stage," the spokesperson said.
The company is trying to find alternative wood supplies, but has so far been unsuccessful.
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