The PTC, originally signed into law by President George H.W. Bush, provides a tax credit of 2.2 cents per kilowatt-hour of renewable power generated.

The letter says the PTC has cut wind energy costs 90 percent since 1980. Wind supplies more than three percent of U.S. demand and accounts for 35 percent of new power capacity installed in the last four years, it says.

Installed wind capacity represents more than $79bn in private investment, according to the letter.

Signatories to the letter also included Akamai Technologies, Annie's, Aspen Skiing Company, Ben & Jerry's, Clif Bar, Jones Lang LaSalle, Levi Strauss & Co, New Belgium Brewing, The North Face, Pitney Bowes, the Portland Trail Blazers, Seventh Generation, Stonyfield Farm, Symantec, Timberland and Yahoo.

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