School absence guidance issued by head teachers' union
New guidance for head teachers in England on the situations in which pupils can be given time off during term time have been drawn up.
A crackdown has seen a rise in fines for unauthorised absences, but parents have said the rules are confusing.
The guidelines have been drafted by the head teachers' union, the NAHT.
Funerals, weddings and religious events will count as acceptable "exceptional circumstances" but cheaper holidays will not be "a good enough reason".
Writing in the Sunday Times, Russell Hobby, general secretary of the National Association of Head Teachers, said the current system had caused confusion among heads.
He said the new guidance - which reportedly has the backing of Education Secretary Nicky Morgan - would also permit time off to see parents returning from duty with the armed forces, and for children with disabilities or special needs who are suffering a family crisis.
Until September 2013, heads in England could grant up to 10 days' leave a year for family holidays in "special circumstances". But now head teachers can grant absence outside school holidays only in "exceptional circumstances".
Mr Hobby said: "The trouble is, we have no consistent definition of an 'exceptional circumstance'. This has led to confusion and a sense of unfairness. Two-thirds of the heads we surveyed found this guidance problematic," he said.
He said the NAHT guidelines would help identify an "event whose timing cannot be controlled and which are great emotional significance to the families involved".
But Mr Hobby said pupils should not be given "extended leave" either side of an event.
He said there had been 60,000 fines handed out to parents for removing children without approval and not all were holidaymakers.
Last week, the Local Government Association said the new rules do not recognise the complexities of family life and head teachers should be allowed to take a "common-sense approach" to term time holidays.
Mr Hobby said: "So what about allowing holidays in term time simply because of the cost? I'm afraid these just don't fit the bill. It's not a good enough reason to damage an education. You cannot easily make up the lost learning at home, and falling behind in class can put children at a permanent disadvantage.
"Those who work in schools share your pain. Many are parents themselves and pay these prices, too. We must tackle this. The government should work with the holiday industry to find a way through."
Local authorities are obliged to instigate fines and enforce legal proceedings on behalf of schools in cases of unauthorised absences.
Parents who take children out of school during term-time can receive automatic penalty notices of £60 per child. This rises to £120 if not paid within 21 days.
Parents who fail to pay could face prosecution and a maximum fine of £2,500 or a jail sentence of up to three months.