Typically, antidumping duties are levied when foreign average prices are below the average cost of production. But that also describes a practice that often emerges as a wholly appropriate response to a softening in demand. It is the rare case that prices fall below marginal cost, which would be a more relevant standard.
In the view of many economists, antidumping initiatives should be reserved for those cases in which anticompetitive behavior is involved. Contrary to popular notions about antidumping suits, under U.S. law, it is not required to show evidence of predatory behavior, or of intention to monopolize, or of any other intentional efforts to drive competitors out of business.