The decision adds to the friction in clean energy trade between the world's two largest economies.
The Commerce Department is already investigating charges that Chinese solar panel makers engage in unfair trade practices and will issue a preliminary decision on duties next month.
The Wind Tower Trade Coalition, a group of U.S. producers, had previously said it was asking for anti-dumping duties of 64 percent on imports from China and 59 percent from Vietnam . .
But in its announcement, the department said China was alleged to undercut U.S. wind tower prices by nearly 214 percent and Vietnam by 141 to 143 percent.
Some Chinese makers of wind towers said on Thursday they oppose the charge.
"We are talking to the China Commerce of Ministry about this," said Wang Debao, a vice-director at Chengxi Shipyard Co, whose wind tower business made up nearly 10 percent of its annual revenue which exceeded $1 billion last year.
"We are hiring lawyers to challenge the allegations," said Wang, whose company is a unit of China State Shipbuilding Corp.
Other Chinese wind tower makers Titan Wind Energy (Suzhou) Co and Shanghai Taisheng Wind Power Equipment also expressed concerns, saying any anti-dumping duties by the U.S. could hurt prospects in a growing market.
U.S. producers also want additional countervailing duties on wind towers from China to offset alleged government subsidies, despite a recent U.S. court ruling that struck down the use of such duties against "non-market economies" like China.
A separate U.S. government agency, the International Trade Commission, held a hearing on Thursday to probe whether U.S companies have been materially harmed or threatened by the imports. The panel will vote next month on whether there is enough evidence of harm for the case to proceed.
Shut Out of Shepards Flat
Imports of the wind towers from China and Vietnam were an estimated $103.6 million and $51.9 million, respectively, in 2010. The towers, which can stretch more than 100 meters into the air, are made of individual pieces assembled on site. They support the blades and housing for the wind turbines.
Kerry Cole, president of Trinity Structural Towers, said domestic producers suffered a severe blow when they were shut out of the 338-tower Shepherds Flat project in eastern Oregon, which is due to be completed next year and is billed as the world's largest wind farm.
"All of it went to China ... This lone lost sale had ripple effects throughout the industry ... After losing this sale, domestic producers were desperate to fill their order books," putting them under tremendous pressure to cut prices, Cole said.
U.S. producers will continue to face "reduced business volumes, margins and reduced profits" unless the United States slaps duties on imports from China and Vietnam, Michael Barczak, vice president of sales for DMI Industries, told the ITC.
"Current production levels are low and because of imports are not projected to improve in future years. If these trends continue, a number of domestic producers will have to shut down plants or consolidate production," Barczak said.
US Suppliers "Unreliable"
Lawyers representing Chinese and Vietnamese producers, as well as the U.S. operations of German manufacturing giant Siemens, argued that demand for wind towers was driven by more than just price.
For wind projects near the coast, it can be cheaper to import towers from Asia than to buy from a U.S. manufacturer and ship them across the country by rail, said Christopher Hauer, director of Siemens tower operations in the United States.
It also is critical manufacturers supply towers on time and to the specifications Siemens needs, Hauer said.
"Domestic manufacturers have proved themselves unreliable and unwilling often to provide supply. Siemens can not afford to be left without supply
