The US has in the past exempted Canadian softwood products that originated from places where 
raw material was acquired at market prices. The Americans have always had a problem with BC because most of the raw material comes from crown land and sold at prices considerably lower than what producers have to pay in other parts of Canada or the USA.
Stumpage fees run somewhere between $15.00 and $22.00 per cubic meter for stud wood and saw logs depending on the species and  supply and demand conditions. The mean would typically be about $18.00. The BC government is selling for as low as $5.00 per cubic meter in some coastal areas.
This is what's causing the issue.