The car park was built so that opera lovers could enter the theatre, near Lewes, East Sussex, without getting mud on their shoes or on skirt hems.
But Lewes council says the new blot on the landscape ruins a site which has been designated an area of Outstanding Natural Beauty - and the work was carried out without planning permission.
The council wrote a letter to Sir George Christie, the chairman of Glyndebourne, saying that the planning committee's decision to start enforcement action was unanimous. Councillors made their decision after being shown a video of how the car park ruins the view from the Sussex Downs.
Councillor Vic Tomkinson, chair of Lewes council's northern area planning committee, said after the meeting: "When they covered the field over, the reason they gave was that the season was approaching and they needed a car park.
"They needed planning permission for what they have done. It is an absolutely abominable stretch of Tarmac which goes across the hillside ... They do seem to have a cavalier attitude to the planning regulations," he said.
"With the opera they are doing something admired around the world ... If they had co-operated with us we could have got something which looked better than this."
A spokesman for Glyndebourne said: "We don't feel we are able to comment until we receive official notification from the council."Reuse content