Protestors are preparing legal action over a reorganisation that would effectively force parents to send their children to a faith school.
Swanage First School in Dorset has been earmarked for closure, despite being the only non-religious school in its area. If the plan is approved, it would be the first time an area with more than one school had failed to provide a non-religious option.
The move has led to a barrage of complaints from the school, local community and secularist campaigners who oppose the imposition of faith-based education.
They say it shows a failure of government policy to widen choice while handing increasing influence to religious organisations.
Jim Knight, the schools minister and local MP, has also spoken out against the plans, saying parents should retain the "fundamental choice" of whether they want faith-based education for their children.
The National Secular Society is now preparing a legal challenge under the Human Rights Act. "The act says that parents should be able to educate children in accordance with their own beliefs," said Terry Sanderson, its president.
"This is often used as the justification for the existence of religious schools. But it applies equally to parents who want their children to be brought up outside of any religion."
Andrew Copson, head of education at the British Humanist Association, which supports the local campaign, said: "If this community school is closed, it gives the lie to the government rhetoric about choice."
Under the law, when a new school is created there must be a competition whereby organisations can bid to run it. But Swanage is set to be the first example in which there has been no bid by a non-religious group, Mr Copson said.
The plan to close the school is part of wider strategy by Dorset County Council to reorganise schooling and cut surplus places.
The council wants to phase out a three-tier system - which includes first, middle and upper schools - and replace it with a conventional primary and secondary system.
Under the plans, Swanage First, rated outstanding by Ofsted, and St Mark's CofE First School would be closed and a new primary opened on a different site.
The council has said any new school would "respect the faith tradition" of St Mark's, even though 10 of the 13 first schools involved in the reorganisation plan are already faith schools.
In a poll of parents at Swanage First, 85 per cent said community status was important to them.
Hannah Etherington, assistant head, said there were also wider concerns. The school is situated in the centre of town, but under the proposals it would move to the outskirts. This would make it more difficult for pupils to gain access to local amenities and mean increased carbon emissions as pupils would be unable to walk to school, Ms Etherington said.
Toni Coombs, Dorset County Council's cabinet member for children's services, said: "The two-tier model is the only option for the area that will reduce 900 out of over 1,000 surplus places and provide a viable, sustainable and flexible school system."
The consultation on the proposals closes next month.