(Bloomberg) -- U.S. solar stocks led by residential installer Sunrun Inc. tumbled after California proposed new rules for rooftop power systems that threaten to slow installations.

Sunrun plunged more than 13% in New York trading on Tuesday, its biggest intraday drop since March, while SunPower Corp. fell much as 9.2% and Sunnnova Energy International Inc. slumped as much as 9.4%.

California regulators proposed sharply lowering subsidies and adding new fees for home solar users on Monday. The subsidies have been a key driver for the residential solar market, and reducing them may force some consumers to reevaluate whether installing panels would make economic sense.

This proposed decision -- if final -- “could wipe out a chunk of the segment of consumers that are buying solar primarily for savings,” Philip Shen, an analyst at Roth Capital Partners, wrote in a research note. It could also “meaningfully cut” installation volumes.

The proposal, which could change before it’s finalized, comes as high prices and supply-chain kinks already threaten the U.S. solar market. Total installations next year may fall 15% from 2021, according to a Tuesday report from the Solar Energy Industries Association and Wood Mackenzie Ltd.

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