(Adds details, background on aluminum trade disputes)
WASHINGTON, Jan 12 (Reuters) - The U.S. International Trade Commission on Friday said in an initial finding that imports of aluminum alloy sheet metal from China harm U.S. producers, allowing a U.S. probe to proceed into whether the product was being dumped or unfairly subsidized.
Employing a seldom-used tactic aimed at speeding up the imposition of duties, the U.S. Commerce Department in November "self-initiated" anti-dumping and anti-subsidy investigations of the imports, which are typically used in construction and in transportation and electrical equipment.
It estimated it would impose anti-dumping duties of about 56.54 percent to 59.72 percent in the case.
About $603.6 million worth of the flat-rolled metal was imported from China in 2016. The probe excludes aluminum used in beverage can manufacturing.
The unanimous vote was applauded by the Aluminum Association, which represents U.S. aluminum producers and worked with Commerce on the probe.
"U.S. companies that make common alloy aluminum sheet have suffered extensive injury thanks to unfairly traded imports from China for many years," the group's president, Heidi Brock, said in a statement.
But the National Marine Manufacturers Association said the decision was bad news for aluminum boat makers, a big part of a $3 billion recreational boating industry that claims to support 650,000 U.S. jobs.
"The ruling is expected to significantly drive up the costs of aluminum used to manufacture more than 111,000 boats such as pontoons and fishing boats, which make up 43 percent of new powerboat sales," NMMA President Thom Dammrich said in a statement.
Earlier this week, U.S. aluminum products makers sought new protections against Chinese aluminum shipped through Vietnam, asking Commerce to investigate allegations that China Zhongwang Holdings Ltd is circumventing U.S. duties.
And next week, the Commerce Department is due to send the White House the results of its investigation into whether rising aluminum imports are threatening U.S. national security, a probe likely to provide U.S. President Donald Trump with an opportunity to levy broad tariffs or import quotas on aluminum.
The results of a similar "Section 232" national security probe into steel imports was given to Trump on Thursday night. Commerce did not reveal its recommendations.
China’s excess production capacity for both steel and aluminum has emerged as a major trade irritant for the United States and Europe, prompting them to consider new steps to protect domestic industries and jobs from a flood of Chinese imports. (Reporting by David Lawder, Tim Ahmann, and Eric Walsh; Editing by Susan Heavey, Tom Brown and Chris Reese)