The promoters of a major music festival - the brainchild of opera star Bryn Terfel - say it is threatened by a rival event starring Will Young and Bryan Ferry.
Bryn Terfel says the Faenol Festival has gained international status
IMG Arts and Entertainments says the August event near the foot of Snowdon could end unless it has a guarantee against possible financial loss.
The company says it is worried by the impact of Summer Pops, which also features the Beach Boys, held seven weeks earlier.
Gwynedd Council says it will decide next week whether to offer extra money on top of a £50,000 already put forward.
The annual festival is due to be held for the fifth time this August Bank Holiday at the Faenol estate, between Bangor and Caernarfon.
Last year's three-day event attracted 20,000 people to see the likes of West End star Elaine Page, Spanish tenor Josť Carreras, and Bryn Terfel, who performs every year.
IMG joint managing director Michael Storrs said the company was in discussion with Gwynedd council seeking a guarantee of £50,000, and added: "Next week is decision day."
Promoters say Faenol fans may choose to see Bryan Ferry instead
This year's festival is due to feature the pianist and BBC presenter Jools Holland and young jazz star Jamie Cullum.
Mr Storrs said the four-day Summer Pops from 9 - 12 July would not be in competition with opera and Welsh pop acts at Faenol.
But he said the "middle-of-the-road audience" may have to choose between Holland and Cullum and alternative attractions at Summer Pops.
"Some of the audience is going to say, 'Can I afford to buy a ticket for Bryan Ferry or will I just go to one night?' " said Mr Storrs.
"We would hate to see a waste of four years' investment. Before, there was no event in that area of a similar nature, and it is shown in different parts of the world.
"Next week is decision day - it depends how much people who make these decisions value the event. Tickets will not go on sale if this problem is not solved.
Mr Storrs said the Summer Pops festival, "has thrown a last-minute spanner in the works which has come straight out of the blue - we are in a crisis situation.
"The crux is that Faenol is one of the most beautiful parts of the world and there aren't one or two million people around the corner - the size of the market has always been a major factor.
"We are rushing around talking to anybody who can help the problem and guarantee against the loss - the council, Welsh assembly and we are talking to commercial sponsors."
Gwynedd Council said it was in "constructive discussions" with IMG.
A Gwynedd spokesperson said the council board would make a decision next Tuesday on the possibility of offering further financial help to the £50,000 already offered by the council-run Gwynedd Events Commission.