Parents claim they have been banned from a school sports day in case it leads to a crush on the playing field.
The head of Glapton Academy primary school in Clifton, Nottinghamshire, this week wrote to parents telling them they were not invited to next month's event because of 'rising pupil numbers'.
But some parents say they were told the school implemented the ban in order to 'avoid another Hillsborough'.
The newsletter from head Ruth Ellis read: "Thursday 3rd July is planned for sports day. Unfortunately, due to rising pupil numbers, we will not be able to invite parents to sports day this year."
Dad David Elliott, 35, whose six-year-old son attends the school, said: "This is bonkers. Simple as that. I rang the school up and spoke to someone who said it was because of health and safety.
"I asked what that meant and the woman said it was because there were more pupils at the school and therefore more potential parents coming on sports day.
"When I asked what the school was afraid might happen she said there was a potential for a crush. I said 'what, like Hillsborough?' sort of as a joke, and she said 'yes'.
"I was gobsmacked. I've never heard anything do ridiculous in my life."
Other parents threatened to boycott the sports day on July 3 in protest at the ban.
Vicky Samson, 32, whose two children Elliott, 11, and Daisy-May, five, go to the school, said: "If we can't watch, then my children will not be taking part in the sports day.
"They manage to cram all the parents into a school hall, but apparently we won't be able to watch on the huge field."
Lisa Darby, 32, whose six-year-old daughter Libby is in Year 1, told her local paper: "Sports day should be a family event and parents should be able to share their child's excitement at taking part in all the races."
However, Nick Ydlibi, chairman of governors, defended the move, saying: "Safeguarding our children is our main priority. We feel that due to the rise in pupil numbers along with the close proximity of current major road and tram works a lot of strangers are in and around our school locality.
"Because of this it would be extremely difficult for us to guarantee the safety of our children at an outdoor event with open gates; this is why this year, this very difficult decision has had to be made."