Opponents protesting a controversial solar plant in California have forced the California Energy Commission to temporarily withdraw approval, Reuters reports.

The Calico Project, a 663.5 megawatt project belonging to NTR Tessera Solar was improperly licensed, according to opponents. California Unions for Reliable Energy wrote the commission earlier this month, claiming Calico had not filed required paperwork about environmental consequences. The Sierra Club may join the challenge, asserting on the behalf of various wildlife.

"We are considering litigation", Sierra Club senior staff attorney Gloria Smith told Reuters in an email.

California mandated power companies to derive one-third of the state's power from renewable sources by 2020. The $2 billion Calico solar plant plays a significant role in that requirement. But now that effort is held up because of pressure applied by opponents. Karen Douglas, chair of the energy commission, issued the order withdrawing approval while noting the commission was not stating it agreed with arguments against the solar plant.

The California Energy Commission pulled back approval this past Friday and the commission will resume dealing with the challenge on December 1.