The decision to begin consultation over the closure of a Bath boys' school is to be reviewed.
Bath and North East Somerset (Banes) Council's cabinet voted to recommend the closure of Culverhay School.
But 27 opposition councillors, both Labour and Liberal Democrats, have now signed a formal challenge calling in the decision.
The challenge must be heard at a meeting of the council's overview and scrutiny panel within 14 working days.
Culverhay School is around half full and had wanted to introduce girls.
'Not on table'
The cabinet said closure was the best solution to help reduce the 800 empty desks at schools across the city.
But opposition councillors said the recommendation "bore no relation" to the preceding consultation which initially proposed shutting down three secondary schools in the city and opening two.
Liberal Democrat councillor Paul Crossley, who is leading the call in, said: "The proposal to close Culverhay was simply not on the table before.
"In fact the consultation showed a clear plan to reopen it as a coeducational school."