The U.S. Commerce Department said on Thursday it was launching an investigation that could lead to steep import duties on more than $100 million worth of wind energy towers from China and Vietnam. 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 manufacturers 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 213.54 percent and Vietnam by 140.54 to 143.29 percent.