The operators of Gatwick Airport have accused rail bosses of trying to "murder" the airport's non-stop rail service to central London.
Trains currently run directly into Gatwick
BAA has criticised proposals that would mean the Gatwick Express would stop at East Croydon - allowing commuters to use it as well as airline passengers.
This would result in airline passengers laden with suitcases fighting hardened commuters for seats, BAA claimed.
But the Strategic Rail Authority (SRA) says the plans would benefit everyone.
BBC transport correspondent Tom Symonds said BAA was furious at the proposed changes to the Gatwick Express, which currently runs dedicated trains between Victoria Station and Gatwick, waiting for airline passengers at each end.
The SRA wants the service to continue on to the South Coast, stopping at the busy East Croydon station, so it can be used by commuters.
BAA says that will lead to tussles between commuters heading for work and airline passengers with their baggage.
The company's written response to the proposals is entitled The Murder Of The Gatwick Express.
But the SRA says the changes will result in more frequent services, longer trains, and more seats for everyone using the line.