A Stroud based community group is taking Gloucestershire County Council (GCC) to court to challenge the legality of a £650 million incinerator contract.
They are claiming the contract for the construction of the waste incinerator, which is located near junction 12 on the M5, outside of Gloucester, is illegal.
The first hearing is starting today at Bristol High Court - on Redland Street - where both the community group and the council will sit before a High Court Judge.
In 2016, GCC re-negotiated the contract with the company responsible for the site, Urbaser Balfour Beatty (UBB), which resulted in a £150 million increase in the cost of the original contract, taking the total to £650 million.
Community R4C claims this was done in secret with no opportunity for other companies to negotiate or tender for the contract which has been signed for 25 years.
The group has set out plans for an alternative waste treatment which could easily deal with waste produced within the county.
This would include a pre-treatment plant which would sort residual, or black bag, waste to recover valuable and recyclable materials.
The group is now demanding that the £150 million is given back to the public.
If successful, the group will be able to pursue the case for between £75 million and £150 million, and the money then returned to Gloucestershire County Council by UBB.
This would lead to substantial changes in the way the plant operates, including more rigorous recycling and protection of the environment.
Thousands of people objected to the building of the incinerator, as well as the whole planning committee.
People in Gloucestershire who oppose the site, have been protesting for more than four years.
Gloucestershire County Council has said that the incinerator will save people money and end landfill.