Tea and coffee could be restricted in schools to pupils over the age of 16 in plans to encourage a healthy diet.
It is an option being considered as part of a consultation exercise by the School Food Trust (SFT).
Teachers' unions say this is another example of official bodies meddling in areas where they should not interfere.
The SFT stresses it has no intention of issuing an outright ban on the traditional "British cuppa".
General secretary of the National Association of Head Teachers Mick Brookes said such advice would cut into people's civil liberties.
He said: "Words fail me.
"I can understand the anxiety about young people eating appropriate food. But this nannying really has to end."
I never thought I'd find myself agreeing with the head of a teachers' union. But I do: it's ridiculous that public money (£21 million of it over the next three years), is being spent on debating such unimportant issues as the amount of tea and coffee that schoolchildren (most of whom tend not to be afficionados of those beverages, anyway) should be allowed to consume.