Posties Park in Dumbarton has been earmarked as the site for a new £20 million Our Lady and Patrick's High School.
But local people, including community councillors, are protesting the moves and a petition calling for the plans to be scrapped has collected more than 1000 signatures.
The controversial proposals will be discussed at West Dunbartonshire Council's Education Services Committee today.
And despite the local opposition, officials from the local authority have recommended them for approval.
But campaigners hope that they can convince councillors to throw them out and preserve the well-used public park for future generations.
They will address members of the committee before they take a vote on the fate of the conservation area. Posties Park is a large piece of open greenspace which sits near Dumbarton town centre, close to the River Leven and the River Clyde.
Rose Harvie, secretary of Silverton and Overtoun Community Council has urged West Dunbartonshire Council planners to look again at alternative sites. She said: "We would like the council to reject this recommendation.
"From a planning point of view, the site is protected by at least three policies in the adopted Local Plan: retention of open space; protection of landscape character; and two separate environmental designations.
"It is an International Nature Conservation Site, and an Inner Clyde Special Protection Area, because of the over-wintering redshank bird species.
"We do not believe that the council should breach its own Local Plan policies."
Campaigners have also raised concerns about traffic congestion and noise and say the build will have a detrimental effect on the surrounding area.
A report by council officials, to be tabled at today's meeting, states that Posties Park could be an "impressive site" for a new school building. It adds: "Locating 1000 young people and more than 100 staff so close to Dumbarton town centre could also result in economic benefits to the town."
Protesters will stage a rally before today's meeting and have urged local people to turn out in support of the campaign.