Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers, said altering the three-term year would be "the last straw that breaks the camel's back".
Margaret Hodge, chair of the Commons education select committee, advocated ending long summer holidays in favour of a four- or five-term year earlier this month.
Local government leaders have also come out in favour of change, to spread holidays more evenly throughout the year.
But Mr de Gruchy said: "This is in response to Margaret 'Holiday' Hodge. It's a load of baloney. If people want to have children that's fine, but I do think there's some onus on parents to spend some of their time with them. People cannot expect schools to bring them up entirely. This is an issue teachers are fed up to the back teeth with."
Mrs Hodge has argued that teachers should have more help with administration in return for extending the 38-week school year. NASUWT members are expected to debate a motion condemning any changes at their annual Easter conference. The union leadership is awaiting the result of a ballot on industrial action over what it claims is excessive bureaucracy in schools.Reuse content