Duane Lugdon of United Steelworkers International says the uncertainty will likely force more workers than necessary to leave the area.
Brookfield Asset Management is the current owner of the mill. It blames high oil prices for the indefinite shutdown earlier this month.
But the company has said it hopes to resume production next year, if an agreement can be reached with a third party to install a biomass boiler.
Katahdin’s sister mill in East Millinocket remains in operation.
18 workers have reportedly been laid off already. More than 200 stand to lose their jobs once the shutdown is completed.