Union leaders are considering legal action against plans to build a City Academy in north London.
Campaigners say City Academies are fundamentally flawed
The National Union of Teachers is stepping up its fight against the Wembley Academy after its backer withdrew his support for the school.
The NUT says its occupation of the proposed site led to businessman Andrew Rosenfeld pulling his sponsorship.
Brent Council is now considering another sponsor after its officers warned a delay threatened the project.
"The NUT is considering a legal challenge against the academy," said Brent NUT campaigner Hank Roberts. "We're fighting this on every front. We're determined to seriously damage this seriously flawed project - if not finish it off completely.
"There's an absolute link between our protests and Mr Rosenfeld's withdrawal of support," said Mr Roberts. "It's not just a coincidence. We're not going away."
Campaigners have been occupying the site of the proposed Wembley Academy since late March and have pitched tents on open land, close to the new Wembley Stadium.
A council spokeswoman said unless the council went ahead with development it would be unable to meet the growing demand for secondary school places in Brent.