Commerce Secretary Ross explained things in a TV interview last night. The Canadian dairy producer monopoly decided to rig the Canadian price of ultrafiltered milk which is a new product not protected under NAFTA. 

The US wanted to send a message to Canada using lumber. Lumber was probably going to get whacked anyway but making the linkage was a warning shot for Canada.

The Liberals and the media cannot report the fact that the Canadian dairy monopoly has cost many jobs in the lumber industry. Canada's stupidity has caused us a major defeat.