Government plans to cut financial incentives for solar electricity will come under challenge at the High Court.
Environmental pressure group Friends of the Earth (FoE) and two solar companies - Solarcentury and HomeSun - are launching an application for judicial review.
They are challenging Government plans to cut feed-in tariff subsidies - payments made to households and communities that generate green electricity through solar panels - on any installations completed after December 12 this year.
FoE says the "premature and unlawful" December deadline fell 11 days before a consultation into feed-in tariffs ends and has already led to unfinished or planned projects being abandoned.
A recent report commissioned by FoE and an alliance of solar firms and consumer and environmental organisations known as "Cut Don't Kill" estimated the allegedly premature cuts could cost up to 29,000 jobs and lose the Treasury up to £230 million a year in tax income.
Construction firm Carillion has warned 4,500 workers their jobs are at risk.
Friends of the Earth's executive director Andy Atkins said: "The Government's rushed plans to slash solar subsidies have pulled the plug on countless clean energy schemes and threatened thousands of jobs - we believe this is not just unfair, it's unlawful.
"We agree falling installation costs mean solar payments should fall, but the speed and scale of these proposals will have a devastating impact on a thriving industry.
"The Government must think again and take steps to safeguard UK solar jobs and help cash-strapped families and businesses to free themselves from expensive fossil fuels."