A debate on the private bill which would enable Edinburgh City Council to build on Portobello Park, formerly designated as common good land, is due to take place at Holyrood today.
It would overturn a ruling by the Court of Session which declared the park's status prevented the council from developing there.
A spokesman for the Portobello Park Action Group said it "strongly supports" the building of a new Portobello High School.
A spokesman added: "However, the park is not the best place to build it and the council itself identified alternatives years ago, but simply decided not to pursue them.
"If the park loses its status as common good land, a dangerous precedent will be set for other green space throughout Scotland. A positive vote would provide authorities with an easy option to bypass legal protection of common good land and take it for any purpose they wish.
"Other Scottish parks that are common good land, such as Bogton Park in Forres, Westerton Park in East Dunbartonshire, Coo's Green in North Berwick and Cowan Park in Barrhead, are already earmarked for development, which will be made easy if this bill is passed."
The Court of Session found in September 2012 that the council had gone beyond its powers when trying to appropriate 25% of Portobello's parkland.