Ryanair has announced 15 new routes from Scotland but the company chief warned some would be scrapped unless the Scottish Government cuts air tax.
Michael O'Leary said new routes from Glasgow and Edinburgh airports would boost growth by 20% to more than five million passengers and were a "demonstration" of the airline's faith in the government's plans to reduce air passenger duty (APD).
Ministers want to cut the levy by 50% by the end of this Parliament before eventually abolishing it but face opposition from the Greens, Labour and the Liberal Democrats.
Mr O'Leary warned that if the law is not passed, he will some move new routes elsewhere.
Speaking in Edinburgh, he said: "We've decided to take Holyrood at its word and assume there will be an APD cut in 2018, and rather than waiting for the APD cut in 2018 we're going to open 15 routes from Edinburgh and two new routes in Glasgow in the winter of 2017.
"We're doing this as a demonstration to the Scottish Government of the benefits that will be brought by Scotland if they go ahead with the promise of a cut in APD."
He added: "The Scottish Government should scrap APD, it is nonsense tax.
"It deters people at the point of entry and taxes that deter people at the point of entry are bad for tourism, traffic and jobs."
Mr O'Leary continued: "These 15 routes will not continue into winter 2018 if the Scottish Government doesn't uphold its promises.
" We will stop growing and investing in Scotland, and we will start growing and investing in other low-tax jurisdictions elsewhere in Europe."
The new routes from Edinburgh fly to Baden, Budapest, Carcassonne, Eindhoven, Hamburg, Katowice, Nantes, Prague, Szczecin, Toulouse, Venice, Valencia and Wroclaw while the two additional Glasgow routes are to Krakow and Madrid.
Mr O'Leary also waded into the debate around another Scotland independence referendum.
He said: "I don't think there will be a second independence referendum north of the border and I think if [Nicola Sturgeon] holds a second one I think she knows she'll lose it. Scotland is not strong enough to stand on its own as an independent economy, not with oil at $50 a barrel."
A Scottish Government spokesman said Brexit was the "biggest threat to Scotland's jobs, prosperity and economy".
He said: "Ryanair's ongoing commitment to Scotland shows the confidence businesses rightly have in our growing economy.
"We are continuing to work hard to ensure Scotland remains an appealing and prosperous place to do business, despite the UK Government dragging its heels in guaranteeing any protection for companies in the face of an impending 'hard Brexit'.
"We are committed to delivering a 50% reduction in the overall burden of air departure tax by the end of this Parliament and abolishing the tax entirely when resources allow.
"This is a fundamental component to boosting Scotland's international connectivity and helping to generate sustainable growth."
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