BAA wants to keep its airports in Glasgow, Edinburgh and Aberdeen
Britain's competition watchdog has given airport company BAA the option of selling Glasgow or Edinburgh airport.
An interim report last year by the Competition Commission said BAA should sell Edinburgh airport.
But the commission's final report has now given the operator the option to sell either of the two airports.
Gordon Dewar from BAA said no decision had been made about whether either Glasgow or Edinburgh would be sold - and refused to rule out an appeal.
The commission added that Aberdeen Airport had to improve consultation with airlines and publish financial information to improve transparency.
It also ruled that BAA must first sell both Gatwick and Stansted airports, and that all three airports should be sold within two years.
BAA has already announced plans to sell Gatwick airport but said it wanted to retain all its Scottish hubs - in Glasgow, Edinburgh and Aberdeen.
The Spanish-owned company currently runs seven airports in Britain.
The commission has said it must sell three of them, including one in Scotland, to increase choice for its customers, both passengers and airlines.
The airports must be sold to different purchasers.
Manchester Airports Group - which owns several airports in England - is reported to be among potential bidders if Glasgow or Edinburgh come up for sale.
BAA's other airports include Heathrow and Southampton.
Christopher Clarke, who chaired the inquiry, said the sale of the airports would bring "substantial benefits to passengers and airlines".
He said: "We expect that the new airport owners, with the operating capabilities and financial resources to develop them as effective competitors, will have a much greater incentive than BAA to be more responsive to their customers."
He added that the airport sales would "kick-start a process of competitive rivalry from a standing start where today there is no competition at all".
BAA said it would consider the terms of the report before deciding how to respond, but it may contest the ruling.
BAA's Gordon Dewar said: "We remain proud of our track record in Scotland, and have delivered substantial investments in both customer service and route development, to the country's clear competitive advantage.
"We continue to believe that the commission's analysis of the Scottish airports market is misguided and its remedies may not be practical in current economic conditions."
Edinburgh Chamber of Commerce said it remained "unconvinced" by the decision to force BAA to sell-off an airport in Scotland.
Chief executive Ron Hewitt said: "We never felt there was an issue of competition (or lack of it) between Glasgow and Edinburgh airports. As far as we could see they serve different markets."
However, he welcomed the ruling to allow BAA to decide which airport to sell.
And he said he was pleased to see plans had been abandoned for rebates on landing charges at Aberdeen Airport.
Glasgow Chamber of Commerce deputy president James Andrew said: "We've supported BAA's focus on investment, customer service and route development.
"It is important for Glasgow and for Scotland that this is maintained, and that stability and long-term growth continues for our airports."
Liz Cameron, chief executive of Scottish Chambers of Commerce, said BAA had invested "heavily" in its Scottish airports over the years, and it was vital this investment was matched or exceeded by any new owner of Glasgow or Edinburgh airports.