U.S. firms, which provide 60% of the solar cells and panels used in India's power plants, are already unhappy with the local content requirements.

WSJ: India Plans Subsidies to Boost Solar-Power Sector

"We believe that restricting imports through measures such as local content requirements only serves to raise prices, limit solar adoption, and hinder the growth of domestic solar industries, in which manufacturing plays a relatively minor role in overall economic value creation, " said a spokeswoman for Tempe, Ariz.

WSJ: India Plans Subsidies to Boost Solar-Power Sector

It is hard for it to raise local-content requirements quickly, since that would change the basis on which companies invested.

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