Ministers have come under attack for dumping a commitment to buy all the government's electricity from clean, renewable energy sources, jeopardising targets to cut climate pollution.

Labour's environment spokesperson, Sarah Boyack MSP, has accused the Scottish government of damaging the vital renewables industry by abandoning a requirement for public sector electricity to be generated by hydro, wind or other forms of renewable power.

Concern has also been expressed by the renewable energy industry and environmental groups. The Scottish government, however, argued that its new electricity contract was aiming to save taxpayers' money.

Ministers have launched a £200 million tender for a contract to supply electricity to every public sector organisation in Scotland. Due to run from next autumn, the contract will include councils, health boards, universities and emergency services.

The most recent three contracts for supplying government electricity, signed by the previous Labour and Liberal Democrat administrations in 2000, 2003 and 2006, all specified that 100% of the power must come from renewables.

But this has been watered down by the Scottish government. Its new tender just gives public sector organisations "the option to buy a portion of green electricity", without saying how much.

To Boyack, this is "outrageous" because it could end up with only a tiny proportion of power coming from renewables. "There is a danger this move could increase the carbon emissions of the public sector overall, and damage the economic viability of our growing renewable energy sector," she said.

"The Scottish government needs to show it is serious about reaching its targets on reducing carbon emissions. So far, all we have had from them on reducing emissions is hot air."

Boyack was environment minister when the 100% renewables requirement was first put in place eight years ago. She argued that abandoning it sent the wrong message to power companies and other major consumers.

She has lodged a series of parliamentary questions seeking to find out more about the government's move. Boyack also pointed out that there was an option to extend the existing contract with ScottishPower for another year.

The green energy trade body, Scottish Renewables, suggested that ministers could be missing an opportunity to cut carbon emissions. "The government needs to use the public purse as a powerful tool to help catalyse the switch to a low-carbon economy, which, in the long run, will deliver cheaper and more secure energy," argued the group's chief executive, Jason Ormiston.

According to Dr Richard Dixon, director of the environmental group WWF Scotland, there were problems with the claims made by some of the providers of green electricity.

But he added: "Changing away from the current 100% deal is clearly giving a confusing signal to the public."

Finance secretary John Swinney defended the move, arguing that a requirement to use only renewable electricity wouldn't work. "Buying 100% green electricity does not decrease emissions and does not increase the production of renewable electricity," he said.

"Market conditions, led by our renewables legislation, mean that the demand for green electricity remains significantly ahead of supply. Paying the green premium' is likely to be more expensive and could even push prices up."

The new arrangements would give public bodies "innovative options" to access advanced metering and small-scale renewable initiatives. This could reduce consumption and cut the cost for Scotland's taxpayers "in a tight financial climate", Swinney argued.

"We want to boost the amount of energy coming from renewables," he added. "It is completely wrong to suggest that our approach to buying electricity will harm that ambition."