A council is considering legal action against Coventry Airport over claims a runway has been extended without permission.
Coventry Airport denies it has breached planning regulations
Airport officials have applied for permission to build a passenger terminal to cope with new budget holiday flights.
Concerns have been raised by residents that work has already started.
Warwick District Council said the airport must justify the creation of a surface which could act as a runway.
At a meeting on Tuesday evening the council said the resurfacing of an area at the end of a runway was unlawful and has asked the airport for an explanation.
The airport denies that any work has been carried out without permission.
Holiday company Thomson announced in December the introduction of a new low-fares airline, Thomsonfly.com, based at Coventry Airport.
The airport will be operating cheap flights to 11 European destinations from next month.
Many local residents have objected to the proposals, claiming they will cause traffic problems, noise and pollution.
The company claims more than 200 jobs will be created at Coventry Airport in the first year.
Warwick District Council will consider plans to build a new terminal in April.