Edinburgh City Council has said it will sue a local protest group for £75,000 to cover costs incurred in their recent legal case against the local authority.
Portobello Park Action Group (PPAG) had taken the council to court to try and halt plans to build a new Portobello High School.
The petition was dismissed by Lady Dorrian as it was entered too late, so PPAG said it would appeal.
The council said it intended to pursue PPAG for their costs to date.
Marilyne MacLaren, Edinburgh City Council's convener of education, said: "There is no doubt that Portobello High School urgently needs replaced and there is huge local support for this.
"PPAG's actions to date have already delayed the opening of the new school and despite Lady Dorrian's judgment clearly supporting the council's position, they continue to further delay the plans for the new school".
Phil Wheeler, the council's convener of finance and resources said: "Enough is enough.
"The council has incurred significant legal expenses to date, in excess of £75,000, and the appeal will incur considerable additional costs.
"We have a duty to Edinburgh's taxpayers to ensure their money is not wasted and we intend to pursue PPAG for their costs to date.
"We will also use all measures available to us to protect the council taxpayer from further expense arising from the ongoing legal proceedings".
The new £41m school was first proposed 10 years ago to replace the ageing 1960s building.
It is to be built next to Portobello Golf Course and feature a 25m swimming pool and sports pitches for community use.
Giselle Baillie, 51, who has children at Portobello High School, said: "I very much welcome the council pursuing PPAG for costs because as a council taxpayer I think they have an obligation to cover the costs they have created.
"This latest action by PPAG is malicious and we think its designed to delay the project indefinitely.
"They know they have lost but now they are trying to cause maximum disruption which will affect thousands of children and could cause the council to have to go back out to tender."