GILLOTTS School is being urged to honour the aims of the joint Henley and Harpsden neighbourhood plan to provide affordable housing.
A playing field at the secondary school is earmarked for about 50 homes in the plan, which was approved at a referendum in March.
The plan names a total of 11 sites for development and says that 40 per cent of homes on each development should be affordable.
The academy’s trustees plan to sell the 8.4-acre field to fund £14million worth of new buildings and improvements.
A meeting of the neighbourhood plan steering group heard that the school was a registered charity and had to get best value for the land.
“They are looking for about £10 million,” said Councillor Sara Abey.
Group chairman Dieter Hinke said: “Clearly this is a land sale which we cannot get involved in, only when developers put plans forward for the site.
“All we can say is ‘please note the neighbourhood plan’. If they sell it to a care home or something it’s not going to work with the plan.
“Every site must develop the elements of affordable. Unless they provide 40 per cent affordable they will not get planning permission.”
The group is to seek advice from the Charity Commission.