Blocking Deadly Fentanyl Imports Act This bill expands reporting requirements related to foreign countries that produce illicit fentanyl and limits assistance to countries that fail to take various actions to combat illegal drug production and trafficking. The President's annual report to Congress on U.S. strategy for controlling international narcotics shall include a section that identifies the countries that are the most significant sources of illicit fentanyl, fentanyl analogues, and precursor chemicals used for producing fentanyl. The report shall also describe the extent to which such a country has cooperated with U.S. efforts to prevent exports of such substances into the United States. The United States shall withhold 50% of the foreign assistance allocated to each identified country for the fiscal year. The Department of the Treasury shall also direct U.S. Executive Directors in each multilateral development bank to vote against making loans or allocating funds to such countries. Both restrictions may be waived if the President certifies that the country has cooperated fully with U.S. anti-drug trafficking efforts or if vital U.S. national interests necessitate such a waiver. The bill also directs the President to identify countries that (1) have not adopted various procedures for countering narcotics production and distribution, or (2) are incapable of prosecuting individuals that manufacture or distribute new types of drugs.