A US lumber company has told the Forest Service it may close a mill unless it is guaranteed an annual harvest of 25 million board feet from Kootenai National Forest.

Stimson Lumber Co, which employs 250 people at the Libby mill, says it must be assured of enough lumber to keep the mill operating. It has given the Forest Service an 18-month deadline to answer the ultimatum.

The Forest Service says it cannot make promises to private lumber companies but said all issues will be looked at in its Kootenai National Forest plan.