In a recent statement, the DOC said the investigations will determine if producers in Vietnam, South Korea, Canada and Indonesia are receiving unfair subsidies.

The dumping margin for Vietnam is 79.96-109.86 percent, and there are 24 subsidy programs for wind towers in the country, it alleged.

The investigations began after the Wind Tower Trade Coalition filed petitions in early July. Its members include leading U.S. wind tower manufacturers Arcosa and Broadwind Energy.

Vietnam exported wind towers worth $21.4 million to the U.S. last year, according to the DOC. The corresponding figures were $37.4 million for Indonesia, $50 million for Korea and $60.2 million for Canada.