Flights are continuing from Coventry Airport this Easter weekend, despite an enforcement notice designed to prevent the use of a passenger terminal there.
Airport bosses say they do not need planning permission
The notice, which takes 28 days to come into effect, was issued by Warwick District Council on Thursday.
The authority says work carried out on the temporary passenger facilities breached planning regulations. Airport managers deny the claim.
Thomsonfly began operating budget services from the airport on 31 March.
The dispute centres on the size of the new development at the airport.
The council says the passenger terminal is big enough to require planning permission - the airport disagrees.
Its managers have said they are prepared to take the fight all the way to the High Court if necessary.
Coventry Airport managing director Bill Savage said: "We think it's disappointing to the numbers of passengers who've already booked and also to the over 360 new staff that have started here.
"It's something of a kick in the teeth when all we've been doing is what's in Warwick District Council's local plan."
Thomsonfly eventually hopes to offer services to 11 European locations.