Thousands of visitors and competitors attend the week-long event
A drugs advisory body has launched a petition against an annual Welsh language youth festival's plan to sell drink to visitors for the first time.
The Welsh Council for Alcohol and Other Drugs said Urdd Gobaith Cymru's move "undermines" assembly government policies to promote health and fitness.
The Urdd, has up to 100,000 visitors and 15,000 competitors, and has £300,000 public sector funding.
But an assembly government spokesman said: "This is a matter for the Urdd."
The 2010 event is being held in Llanerchaeron, Ceredigion, in May.
Selling alcohol has always been prohibited on the main field at outdoor Urdd eisteddfodau, but organisers now intend to sell drink with food.
The drugs council says it wants the assembly government to consider only funding future Urdd eisteddfodau on condition that alcohol is not sold on the eisteddfod site.
Chief executive Wynford Ellis Owen said its opposition was based on the festival being for children and young people, so the great majority of competitors and their friends would be under the legal age for alcohol consumption.
He said: "Evidence suggests that children and young people are more likely to become drinkers and heavy drinkers the more society normalises the use of alcohol - which is exactly what the Urdd is doing by introducing alcohol to the eisteddfod site.
"Would the Urdd promote the sale of tobacco on the eisteddfod site?
"It is a frightening fact that Welsh 11-15 year-olds drink more alcohol than those of a same age in any other European country.
"This impairs their health, places them in all sorts of danger and damages their hopes for the future. This is totally contrary to the praiseworthy aims and intentions of the Urdd."
In October 2008, a long-term funding deal to secure the future of the Urdd was announced.
Both the assembly government and the Welsh Local Government Association (WLGA) pay £150,000 to the Urdd in order to help pay towards the costs of running the organisation's annual eisteddfod event.