The U.S. has made a "request for consultations" about Canada's tariff-rate quotas. James McCarten, Canadian Press Bloomberg Creative via Getty Images WASHINGTON, D.C. — The United States opened a new chapter Wednesday in the book of trade tensions with Canada, formally complaining that U.S. dairy producers are being unfairly shut out of markets north of the border. An anodyne-sounding “request for consultations” is actually the first step in what could be the first full-blown trade dispute between the two countries since the U.S.-Mexico-Canada Agreement took effect in July. At its core is how Canada has distributed its tariff-rate quotas — the quantities of certain dairy products like milks, cheeses, powders, yogurt and even ice cream — that can be imported at lower duty levels.