A government subsidy to improve air links from Scottish airports is to be challenged by environmental pressure groups.
Air travel growth is a hot topic
The Scottish Executive has promised to spend £6m over the next three years to lower landing fees at Scotland's airports.
Airport Watch and Transform Scotland said this amounts to state aid to industry and will ask the European transport commissioner to rule the scheme illegal.
They said it was a waste of money to encourage polluting planes to fly what will be under-used and unprofitable routes.
What is the point of subsidising a route that will never make money?
Jeff Gazzard Airportwatch
But Transport Minister Nicol Stephen told BBC Newsnight Scotland he was confident it would withstand any legal challenge.
He said: "The Scottish Executive would not do anything if the advice it was given was that it was illegal.
"This is a sensible, but relatively modest use of executive resources that's already paying dividends."
First Minister Jack McConnell announced the route development fund in February.
He said it would allow the country's airports "to attract a bigger share of Europe's air travel boom".
The scheme, aimed at business and in-bound tourism routes, offers landing charge discounts to airlines opening up new routes to and from Scotland.
The first minister said the initiative would help Scotland win "its fair share" of European tourists who use low-cost airlines to take short breaks.
Jeff Gazzard, the national director of Airportwatch, said that airports operator BAA should be spending its own money to develop routes.
He said: "This is £6m to an industry that does not really need it. Scottish airports make money.
"What is the point of subsidising a route that will never make money? And what is the point of subsidising a route that could be highly profitable?"
Mr Gazzard said that there was already plenty of opportunity to fly to Scottish airports and the current rate of growth in air travel was unsustainable.
He made his call as the Scottish Parliament debated the possibility of expanding one or both of the airports in Glasgow and Edinburgh.
Jack McConnell unveiled the route development fund
A motion from Scottish National Party MSP Sandra White called on the UK Government not to put Scotland's long-term economical prospects at risk by opting to develop only one of the country's main airports.
She said the executive should make representations to Westminster to ensure that the necessary investment is made available for both airports to realise their full potential.
Green MSP Chris Ballance said that the idea of increased air travel was against the executive's declared commitment to sustainable transport development.
The South of Scotland MSP said air travel might not be growing at the present rate if the airlines and their customers had to pay for the cost of the damage to the environment.
He said that an exemption from Vat on flights prices and no tax on aviation fuel amounted to a £10bn subsidy for the airline industry.