Renewable energy groups this week launched legal action against the Mexican government over regulatory changes that local wind and solar bodies said “destroy” project values and undermine confidence, with an impact on $9bn of investments.

The generators – which include global giants Enel and EDF, according to Bloomberg – are up in arms over proposed changes to rules for granting the tradable Clean Energy Certificates (CELs) that power users buy to help meet renewable share mandates. EDF has been contacted by Recharge for comment. Enel declined to comment.

Mexican energy ministry Sener recently unveiled plans to widen the eligible base of projects from new generation projects to legacy plants, including hydro and nuclear facilities, said a joint statement from wind association Amdee and solar body AsolMex.

Critics fear widening the pool for CELs would send the value of the certificates plunging, retroactively undermining the economics of projects.

The industry bodies said the generators, which are not identified in its statement, have lodged injunctions against the changes to CELs, which they described as “the main mechanism for Mexico to achieve its national and international goals for clean electricity generation and to meet the obligations of climate change mitigation”.

They claimed the move would also threaten the spectacular price falls that drove Mexican renewable power below $21/MWh.

Mexico’s previously buoyant renewable energy sector has been in turmoil since without any warning, centre-left president André Manuel Lopez Obrador (AMLO), scrapped government tenders soon after taking power in late 2018.

The move came despite the success of a rolling series of tenders which had contracted 7GW of solar and wind at steadily declining prices.