Overseas performers have pulled out of the Llangollen International Eisteddfod, claiming they cannot afford visas which have doubled in price.
500,000 overseas competitors have performed in Llangollen in 60 years
Groups from the Ukraine, Turkey and Indonesia say the work-free permit visas, at £86, are beyond their reach.
Organisers fear the extra costs could mean more groups pulling out and have appealed to the UK government for help.
A spokesperson for the Foreign Office said visas receive no subsidy from tax payers and the costs were necessary.
The 60th Llangollen eisteddfod runs from 4-9 July, and features opera stars Bryn Terfel and Katherine Jenkins.
Until last year competitors had to pay £35 per head for a travel visa or a work-free permit visa.
But since last summer UK Visas have changed the rules and now charge £86 for a work-free permit, which is what a cultural group like a dance troupe or choir wanting to enter the UK must now have.
Visa costs are keeping some performers away, organisers say
One 40-strong group from Turkey has pulled out after being told they had to pay 285 new Turkish Lira per head for a visa - around £100 - for their five-day visit to Llangollen.
Two groups from the Ukraine have decided against coming - one going to a cultural festival in Spain instead of Wales. The average monthly wage in the Ukraine is £50.
Festival organisers say that, despite the visa changes, many large groups of performers will still appear at the event.
But they say the extra costs go against the spirit of the Llangollen International Eisteddfod.
Chief executive of the festival Gwyn L Williams has asked the deputy head of UK Visa to intervene as quickly as possible so that exceptions can be made for the performers.
The Eisteddfod's president Terry Waite has also written to the prime minister while local MP Martyn Jones says he has requested an urgent meeting with the Foreign Office.
The festival was nominated for a Nobel Peace Prize in 2004
A spokesperson for the Foreign Office confirmed the cost of a UK 'permit free' visa increased in July 2005 from £36 to £85.
The spokesperson explained that as UK visas receive no subsidy from the tax payer, the full cost of the worldwide visa operation must be met through fees.
The spokesperson said: "By increasing the visa fee we ensured that we are resourced to maintain our performance level. Before 2005 the permit free visa had not increased in nearly ten years."
The spokesperson added that through a previous cultural agreement with Romania and Bulgaria the visa section in embassies in Bucharest and Sofia had been asked to wave visa fees on this occasion.
The Llangollen International Eisteddfod, which was nominated for a Nobel Peace Prize in 2004, brings performers from all over the globe to compete in singing and dancing - as well as attracting thousands of spectators to the evening concerts.
Organisers say more than 500,000 overseas competitors have performed there in 60 years, watched by around three million spectators.
Bass baritone Bryn Terfel will open this year's festival with his first performance on the Llangollen stage in a decade and mezzo-soprano Katherine Jenkins will perform in the closing concert.
The festival will also feature four of Charlie Chaplin's classic silent movies set to a new score by composer Carl Davis.
Previous performers include Luciano Pavarotti, Nigel Kennedy, Shirley Bassey, James Galway, Lesley Garrett and Michael Ball.