The duties were imposed on steel products produced in South Korea and Taiwan, shipped to Vietnam for minor processing, and then exported to the United States, the department (DOC) said in a statement.

The agency had found corrosion-resistant steel products (CORE) and cold-rolled steel (CRS) produced in Vietnam using South Korean- or Taiwanese-origin substrate, which circumvented U.S. anti-dumping and anti-subsidy duties, it said.

The ruling was partly based on the high growth in steel shipments from Vietnam after Taiwanese and South Korean suppliers were hit with high preliminary duties on their products.

Shipments of CORE steel products from Vietnam to the U.S. increased 4,353 percent from $23 million between April 2012 and December 2015 to $1.1 billion from January 2016 to September 2019, when preliminary duties were imposed on South Korean and Taiwanese products, the DOC said.

Shipments of CRS steel from Vietnam to the U.S. rose 922 percent from $49 million between January 2013 and February 2016, when preliminary duties began to apply to CRS products from the two countries, to $498 million between March 2016 and April 2019, it added.

This is not the first time the U.S. is imposing duties on Vietnamese steel containing foreign substrate.

In 2017, the DOC applied anti-dumping rates of up to 199.43 percent on Vietnamese galvanized steel products found to have been processed from Chinese hot rolled steel, and rates of up to 265.79 percent on CRS steel found to have originated from China.