The Brighton Festival Club has been ordered to cut out late-night noise or face a huge fine.
The club is in the Spiegeltent, put up in Brighton's Pavilion Gardens for the three weeks of the festival.
Celebrities such as Sir Ian McKellen and actress Carol Cleveland and Brighton and Hove City Council chief executive David Panter have enjoyed partying with friends at the club.
The council's environmental protection team has issued a noise abatement order on festival organisers and the owners of the tent after complaints from two people living nearby.
Now live music is banned after 10.30pm, a DJ has been replaced by quieter, taped music and dancing is discouraged.
The order has not affected the daily programme of events in the tent.
The notice was served under the 1990 Environmental Protection Act.
Officials monitored sound levels after receiving a complaint from a resident after the opening party on May 1.
They spoke to tent owner David Bates and it was agreed he would take away two loudspeakers and change the position of others.
Officers visited the tent two days later and more speakers were taken out. The order was issued on Friday and brands the tent a statutory nuisance "by reason of noise resulting from loud music".
It has been served on Mr Bates, festival manager Jane McMorrow and Nick Dodds, chief executive of the festival, and threatens them with a fine of up to £20,000 if they do not comply.
Mr Bates said: "We are angry because we have worked with the officials and done everything they asked. I would have thought they would have used their discretion. It is up to the council officials to decide whether the order should be served.
"This is the first time in the 85-year-old history of the tent we have been served with a noise abatement order. Many residents living in the centre of Brighton have been enjoying themselves in the tent and attending the late-night party.
Mrs McMorrow said: "This raises issues about what we can and cannot put on at future Brighton Festivals. I am sorry the council felt it needed to act.
"Lots of people have signed an impromptu petition calling for the music to be turned up.
"It takes 21 days to appeal, which would bring us to the end of the festival, so there is just no point.
"We feel powerless about the whole thing and if we don't comply they'll seize the equipment and we'll have no music at all."
Carol Cleveland, best known for her roles in Monty Python's Flying Circus, said: "It is a great shame people have complained.
"This is festival time in Brighton and the club created a fantastic atmosphere. The music was not loud rock, it was jazz-based disco with a few Sixties and Seventies numbers."
Broadcaster Simon Fanshawe said: "It is festival time. Any resident who complains about something like this should not be living in the centre of a city."
City councillor Delia Forester said: "I cannot understand it. If residents don't like the noise of central Brighton they should move somewhere else, like Burgess Hill."
Youth worker David Nimmo, 27, a resident at Regent House, which overlooks the Pavilion, said: "We can hear the music from the tent but we know it is only here for three weeks.
"Nobody has been round the flats with a petition or anything. All you have to do if you want to cut out the noise is shut the windows."
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