Also, legislation proposed in the U.S. House of Representatives would effectively blacklist Iran's entire energy sector as a "zone of primary proliferation concern," and prohibit most energy-related trade with Iran.
Mark Dubowitz, an executive director at the Foundation for Defense of Democracies, which campaigns for sanctions against Iran's nuclear program, estimates that sanctions on National Iranian Tanker would lead to a new reduction of 20% to 25%, or 100,000 to 150,000 barrels, per day. That is because Japan, South Korea and India would further cut their imports from Iran, he said.
But Trevor Houser, a director at New York research firm Rhodium Group, said such move could hit Iran's trades with its largest remaining customer, China.
Also, if the tanker company was "designated as an entity supporting terrorism or proliferation, that would put Chinese companies buying Iranian oil at significant risk" of sanctions because of their U.S. investments, said Trevor Houser, a director at New York research firm Rhodium Group.
China could use its own tankers "but they would still need to find a way through the shipping insurance problems created by EU sanctions," Mr Houser added.