Thousands of pupils could miss out on "vital" outdoor learning experiences if planned council cutbacks get the go-ahead, according to a leading provider.
Gwent Outdoor Education Service, which is partly funded by four local authorities in south-east Wales, says its future is in jeopardy because the largest partner, Newport City Council, wants to make savings to its education budget.
The council's cabinet is proposing to withdraw the pound;142,000-a-year subsidy it provides to the service as part of wider cuts.
Ian Kennett, head of the service, said the move could treble costs for users and possibly lead to the closure of two of its three outdoor learning centres.
The service was set up in the early 1970s by the former Gwent local authority to provide "outward bound" residential trips for pupils.
Following local government reorganisation in 1996, a collaborative arrangement between Blaenau Gwent, Newport, Monmouthshire and Torfaen councils allowed it to continue operating.
Currently, the four partners collectively contribute an annual subsidy of around pound;400,000 towards the total pound;900,000 running costs, with Newport contributing the biggest share.
Annually the service provides more than 19,000 "user days" - one person using the service for one day - of which more than 6,000 are provided to pupils from Newport. Some 43 of its 49 primary and secondary schools are regular users.
Mr Kennett said there could be a number of potential knock-on effects if Newport withdraws its cash.
"Charges for a five-day stay for primary pupils could increase by at least pound;100 to pound;265, and the lack of additional financial support available to those eligible for free school meals could mean charges to these children more than trebling," he said.
"Such increases could result in parents being unable to afford the service, while at the same time school budgets would be either insufficient or under huge pressure to subsidise costs."
He said that the financial instability resulting from losing the support of the largest of the four partners could force the closure of at least one and possibly two of the three centres.
"The ultimate losers would be the children and schools who currently benefit from the service," he added.
There are currently around 40 outdoor education centres in Wales, many of which are facing a similarly uncertain future.
Centres in Caerphilly and Powys have recently closed and several that are run and funded by English councils are also under threat.
Although outdoor education is not a statutory requirement, many of the adventurous activities the centres provide help pupils to achieve the requirements of the national curriculum for PE introduced in Wales in 2008.
Alistair Cook, national chairman of the Association of Heads of Outdoor Education Centres, said councils should continue to invest in the "vital" service.
"For the sake of a few tens of thousands of pounds, you are losing vital learning experiences. In big-picture terms the contribution is relatively small, but cutting it has a disproportionately negative outcome.
"It's not just the experience - we will lose qualified, highly-motivated and competent staff. Outdoor education is deemed easy to cut because there's nothing on the statute books that says it has to be delivered."
A Newport council spokesman said it is facing "severely challenging economic conditions" and needs to make savings while continuing to provide the best possible services.
"One of the (cost-saving) proposals is to no longer subsidise outdoor education facilities. This is a non-statutory service and (we are) discussing how this reduced contribution will be delivered with the other contributing councils.
"The Outdoor Education Service is widely used by Newport schools and we want that to continue, but we have to consider whether it is appropriate to subsidise this service in the light of the current financial circumstances."