Organisers of a Herefordshire music and arts festival have been warned they risk a £20,000 fine and prison sentence if the event goes ahead unlicensed.
Up to 5,000 people were expected to attend the free annual Jamstand festival in Ross-on-Wye on 13 and 14 August, the organisers' website said.
Herefordshire Council and West Mercia Police said the event needed a premises licence or temporary event notice.
They said the application deadline had passed and the event must be cancelled.
Jamstand Organisers were unavailable for comment.
This year's event was due to be the fourth annual festival, headlined by Roots Manuva and Ugly Duckling.
Jamstand supporters have created a group on Facebook, called "We want the Jamstand 2010 to go ahead", which has hundreds of members.
Paul Nicholas, the council's assistant director of public health, said: "Licences are essential for events such as this as they ensure the right measures have been taken by the organiser to keep the public safe and also prevent any public nuisance.
"If the event were to go ahead it would be an unlicensed event which is a criminal offence."
Herefordshire Council said it had been in discussion with the festival organisers for several months about the application but had not received one yet.
The deadline for the premises licence was 16 July. It said a temporary event notice could have been applied for, to hold an event with less than 500 attendees, but the deadline for that had passed on 2 August.
It said it wanted to support local events and festivals and invited Jamstand to work with the council and police to stage the event later in the year.