The Government has come under fire for delaying an announcement on subsidy levels for renewable energy projects.
Ministers had been expected to reveal new support levels for projects from April next year. But the Department of Energy and Climate Change (DECC) said it was still "discussing and finalising" details.
Labour's shadow energy minister, Tom Greatrex, claimed investment in clean energy would grind to a halt unless ministers "end the dithering".
Scottish Power also expressed concern, arguing that sticking to the timetable was key to investor confidence.
The DECC was due to announce the outcome of a review into renewable obligation certificate (ROC) banding, a system which obliges electricity companies to buy a certain amount of their electricity from renewable sources.