The president's order came after an investigation into the wind farms by the US Committee on Foreign Investments (CFIUS) said there was no way to mitigate the national security risks posed by the Chinese company's plans.

BBC: US blocks Chinese firm's investment in wind farms

Foreign firms attempting a takeover or merger that might affect national security must get a stamp of approval from a little-known group called the Committee on Foreign Investments in the United States, a panel of representatives from across the government run by the Treasury Department from its grand building on Pennsylvania Avenue, next to the White House.

NPR: Can Next President Deliver on Promises of 'Change'?

An interagency panel called the Committee on Foreign Investment in the United States, which looks at foreign investments for any national-security risk, has informally adopted what one official calls a "hard-look doctrine" toward any Russian attempts to invest in critical American industries.

WSJ: Russia's Deripaska Faces Western Investigations