Passengers have been left stranded after the UK flight ban
A teachers' union has urged schools not to penalise teachers who fail to return after the Easter holiday because of flight suspensions due to volcanic ash.
The NASUWT said many teachers due back in school later were stranded abroad.
Most schools had arrangements to deal with this kind of emergency, but there had been reports one authority aimed to dock pay from absent teachers, it said.
A spokeswoman for the Department for Children, Schools and Families said it was "monitoring the situation closely".
NASUWT general secretary Chris Keates said school leaders would have to determine if a school could stay open or if staff shortages were so severe it would have to close.
But she said: "Reports have already emerged that one authority in the West Midlands, Coventry, apparently has stated that teachers who fail to report to work will be docked pay and expected to reclaim it from their travel insurance.
"This situation is affecting workers and workplaces nationally and internationally. To single out teachers is totally unreasonable and unnecessary.
"Employers should be warned that they are vulnerable to a legal challenge for unlawful deduction of salary if they seek to penalise teachers in this way."
However, Councillor John Blundell, Coventry City Council's cabinet member for children, learning and young people, said he was not aware of such a policy at the authority and did not yet know how many teachers would be affected.
The Department for Children, Schools and Families spokeswoman added: "Schools have contingency plans in place and head teachers are best placed to decide how to cover for absent staff effectively and support pupils forced to miss classes."
Two week wait
Among those stranded because of volcanic ash drifting from Iceland are four teachers, along with 40 pupils, from Orleans Park School in Twickenham, south London, who are stuck in Shanghai, China.
Some 200 students are also stranded in Hangzhou and Beijing.
Jerome Bertin's son is one of the children stuck in Shanghai.
He said the pupils, aged 15 and 16, had been due to fly back on Thursday but were told by a passenger on the same British Airways flight that they would not be able to fly before 26 April.
Mr Bertin said: "We have already looked to see if my son can get back overland and there is a train service from Beijing via Moscow, Copenhagen and Eurostar but it takes 10-12 days. He may have to do this sooner or later."
The school's head teacher is due to meet parents of the stranded children on Monday.
One teacher who will not be at school following the Easter break is Cassandra Williams.
She was due to start her new job as head teacher of Thurton Primary School, in Norfolk, on Monday but is currently in Hong Kong.
Ms Williams had been in Australia for her brother's wedding.
Her airline - Qantas - has said she can stay in a hotel, fully funded with three meals a day.
She said: "There are at least three more head teachers on my flight and I have talked to at least eight general teachers. None of us will be back to school in time.
"There are lots of children meant to be taking GCSEs and A-levels and they are very worried about when they might be able to fly to get home. There were a couple of children who missed exams in January because they were caught in the snow."
University students, approaching the critical point in their courses when deadlines and exams are nearing, have also been affected.
Danielle Dodds, 20, and her friends Hannah Harrison, Monica Black and Laura Shearer are among 100 students from universities across the country who are stranded in Hangzhou and Beijing on a government-funded programme which provides students with experiences of China.
Danielle said she and her fellow students were meant to fly back to the UK over the weekend but had been told that the next flight would be in two weeks.
"As students, some of whom are at crucial points in their degree, we have dissertation deadlines exams and other commitments which we will not be able to fulfil," she said.
Aside from the impact on their studies, the Northumbria University student said there was the more pressing matter of bureaucratic problems to contend with.
"Our visas will run out this week and we have been told in order to extend them we will each have to open a Chinese bank account and put the equivalent of £2,000 in it which little of us have," she said.
"The visas might take days to process during which time our passports will no longer be in our possession which may make getting home even more difficult."
Danielle said the group had been forced to pay for accommodation and living costs themselves.
"Having already spent three weeks here, most of us are running out of money."
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