Disadvantaged children should be allowed to go on holiday during term-time because their parents can't afford the high cost of travelling during school breaks.
The National Union of Teachers (NUT) said holidays away shouldn't be 'the preserve of the middle classes'.
The union said that poor children - defined as those eligible for free schools meals – shouldn't have to miss out on holidays away or risk being fined if they give their kids a break that only richer families are able to afford.
Christine Blower, the NUT's general secretary, said: "It can't be right for children whose parents have less resources to never manage to go on a holiday just because they can't afford to go in the school holiday time."
Under rules introduced in September 2013, heads are now only able to grant leave in 'exceptional circumstances' and parents can be fined £60 per pupil for taking term time holidays without permission.
Ms Blower said: "Holiday companies jack up the costs during school family holidays and the upshot of that is that if you have a reasonable disposable income you can afford to do so. But if you are a family with no disposable income and - we know the poor are getting poorer - then they are going to miss out.
She said family holidays 'shouldn't be the preserve of the middle classes', adding: "Holidays can provide valuable experiences and outdoor learning opportunities. Giving families time to be on holiday together will also have social and emotional benefits which can be of lasting value and support to schoolchildren."
A resolution due to be debated by delegates at the NUT's annual conference in Liverpool this Easter, argues that the regulations unfairly impact on working parents, especially the low paid.
It says: "Conference understands that taking children on holiday is not the same as persistent truancy.
"Holidays can provide valuable experiences and outdoor learning opportunities. Giving families time to be on holiday together will also have social and emotional benefits which can be of lasting value and support to schoolchildren."
It adds that it is not just a problem of high costs impacting on working parents, some are unable to take leave during school breaks due to shift or rostered work.
It calls on schools to interpret the current rules in a way that lets parents take time off during term in 'exceptional circumstances' where both parents and their children agree to catch up on schooling missed.
More on Parentdish: The current rules on term-time holidays