The union, whose members include school meals staff, is concerned that children are being offered poor-quality meals that may increase their exposure to the risk of BSE. It wants education authorities and catering departments to consult parents and schools more widely about menus generally, and beef in particular.
According to Unison's deputy head of local government, Virginia Branney, the standard of school meals has fallen since statutory controls were abolished in 1980.
"Given that for many children, school meals are the only hot meals they get, children from low-income families are having to eat poor-quality food," she said.
Unison blames competitive tendering for driving down costs, and wants the system abolished. It is backing calls for a national food policy to ensure the dietary needs of people on low incomes are met.
The concerns emerged at a seminar in London for Unison members affected by the BSE crisis. Marion Ritchie, of Unison's school meals occupational forum, said schools in her education authority, Fife, had withdrawn pies, sausage rolls and beefburgers, but were still serving liver, haggis and black pudding.
"It is a low-income area and some of the these children have never eaten a piece of meat in their lives. They don't have the age or information to say, 'We're not going to eat beef'," she said.
Dr Stephen Dealler, a consultant microbiologist, claimed that for every cow removed from a herd because it was infected, seven more went into the food chain undetected.
Advice from the Health and Safety Executive and the Department of Health made it clear that people working with animal carcases faced a high risk of infection, the seminar was told.
It was possible that school meals staff could develop the human version of BSE if they came into contact with contaminated meat. "The risk might be very small, but we should know rather than assume everything is OK," Dr Dealler said.