A community group is taking Gloucestershire County Council to court over an incinerator contract now worth £600million.
Community R4C claims the contract for Javelin Park was unlawfully awarded, resulting in a massive rise in costs to taxpayers and a breach of procurement law.
The council says it has followed the law throughout the process.
Protestors gathered at the site at Javelin Park earlier this month when it emerged the project is more than £100million over budget.
They say there are cheaper and better alternatives to the incinerator.
Gloucestershire County Council says, once it's up and running, the incinerator will save taxpayers money.
The council has acknowledged the claim and says it is still reviewing its response.