This question has been rumbling in my head for some time, but was prompted by an article about taxi drivers striking due to an airport surcharge on their passengers. I don't fly often but know those who do, and there seems little effective choice but to pay charges for using an airport's proximal 'drop-off' area/zone; public transport may be variable, or infeasible, pedestrian access is poor, etc. In reading around this question, I see it has been debated in parliament, discussed on motoring forums, mentioned by motoring organisations (by way of the news), and questioned by industry groups (PDF).
Some factors / assumptions considered:
I imagine that by entering such an area one implicitly agrees to a contract to pay whatever charge there is for using it; I am not sure if an unexpectedly large charge (by that I mean one which a reasonable person would find surprising and/or refuse to pay if known in advance) might give rise to claims of unconscionability.
I also imagine that airports, given regulations surrounding their operation and the impracticalities of creating a competing major airport, might be treated as de facto monopolies.
I will assume for the purposes of this question that airports comply with provisions for mobility/disability issues; and that any other gratis areas for unloading motor passengers, however remote, are a beneficent courtesy graciously extended to users of the airport. Similarly, that any driver who is not using the area but accidentally enters it will have their fee voided or waived.
It seems that introducing and/or raising fees is a relatively easy way for airport management corporations to raise revenues. Maintaining effective throughput is sometimes mentioned by way of justification for such fees.
Can an airport set the fee for using a 'drop off zone' to be arbitrarily high? Can this be done at any point in time?