Step 1: Definition of non-tariff barriers (NTBs).
Non-tariff barriers are trade restrictions that are not in the form of tariffs (taxes on imports). They include quotas, licenses, standards, and regulations that indirectly restrict trade.
Step 2: Examine each option.
- (A) Voluntary export restraint: A classic NTB where exporting countries limit shipments voluntarily.
- (B) Procurement law favoring domestic goods: This is also an NTB since it discriminates against foreign producers.
- (C) Sanitary and phytosanitary measures: These are NTBs applied on agricultural imports, often under health and safety standards.
- (D) Antidumping law: This is a trade remedy against unfair pricing (dumping) and not categorized as a non-tariff barrier.
Thus, the correct answer is (D).