Police have confirmed they will enforce new liquor licence regulations at the Splendour in the Grass festival this weekend, meaning anyone younger than 18 will have to be accompanied by an adult.
Last week the Liquor and Gaming Authority included the condition for minors to be accompanied by a responsible adult as part of the festival's liquor licence.
The rule previously applied only to those younger than 16.
Superintendent Dave Roptell, Commander of Tweed/Byron Police District, said fines could be issued to anyone caught flouting the rules.
"If anyone's breaking the law, we're there to enforce it," he said.
Superintendent Roptell said 100 police officers from around New South Wales would be roaming the festival to ensure compliance through "high-visibility policing, being proactive, engaging with and stopping people".
'Heavy-handed' move, organisers say
Festival co-founders Jessica Ducrou and Paul Piticco said they were shocked and disappointed by the liquor licence decision.
"It's unfortunate that such conditions were put in place so close to the event," Ms Ducrou said.
"Historically we've not had any issues with the 16 and 17-year-olds.
"They've been very respectful of being at Splendour and I do think it's very heavy-handed conditions, so we will be discussing that after the event."
Ms Ducrou and Mr Pitacco said they appealed the decision but notified ticketholders as soon as possible when that "process was exhausted".
"Every year a negotiation takes place with Liquor and Gaming," Ms Ducrou said.
The last minute change affects about 2,000 people.
Refunds were offered to those who could not find an adult to accompany them, but organisers said no extra tickets were allocated to ensure minors could bring an adult to adhere to the new rules.
"There's a resale facility where people are able to purchase a pre-loved tickets from another attendee that can't make it for whatever reason, so [tickets] are available, but we haven't increased the capacity," Ms Ducrou said.
"I'm concerned for the 16 and 17-year-olds who were looking forward to an experience that has now changed for them.
"We'll do our best to make sure that everyone is having a good time, is safe and is smooth."
Despite his frustration with the decision, Mr Pitacco said he was confident the event would go ahead without issue and was excited to see the festival return after three years.
"There's been a lot of build-up to this," he said.
"We've gone through a lot as a community and as a music industry.