The Swiss parliament has rejected a controversial air transport accord with Germany, aimed at ending a long-running dispute over noise pollution.
The House of Representatives discussed the agreement on Wednesday.
But a broad alliance of opponents argued the deal, reached between the Swiss transport minister, Moritz Leuenberger, and his German counterpart, Kurt Bodewig, would jeopardise the future of Switzerland's main airport of Zurich.
Under the accord, struck last October, both sides agreed to cut by a third the number of flights permitted to use airspace over southern Germany used as an approach to Zurich airport.
The deal also includes a ban on night flights and a reduction in weekend aircraft movements.
Germany has threatened to unilaterally introduce even tougher measures if Switzerland fails to approve the deal.
A clear majority in the House of Representatives was widely expected to vote against the treaty. The Senate is expected to follow suit at a later stage.
The opponents, including the Swiss Business Federation, the national airline, "swiss", as well as the Zurich cantonal government and airport authorities, all argue the deal is not compatible with European Union regulations.
They also accuse the government of giving in to pressure from Germany. Opponents also believe Swiss authorities would stand a good chance of challenging the threatened German sanctions in court.
Accepting the terms of the accord would put an unfair burden on the population living around the airport, they say.
The government, for its part, says failure to approve the accord would result in considerable uncertainty for Switzerland's aviation and for Zurich airport as an international hub.
Transport Minister Leuenberger stressed that the deal was a fair compromise, because Switzerland had managed to negotiate a deadline of more than three years before the accord would take effect.
However, if Germany makes true its unilateral threat, the number of flights over southern Germany would be immediately reduced to 80,000 per year.
In addition, the Swiss flight control authority, Skyguide, would no longer be allowed to manage incoming Zurich-bound flights over southern Germany.
Some experts say this could weaken aviation around Zurich, turning it into a provincial port. Zurich airport sits less than 20 kilometres from the German border.
Several towns in southern Germany have complained for years about noise pollution out of the airport, and have called for the use of alternative flight lanes into Zurich.
Environmental groups and local authorities from within Switzerland have also voiced concerns about the planned increase in flights under the deal with Germany.
Germany's parliament is expected to approve ratification of the air transport deal with Switzerland in coming weeks. Political analysts say the ruling coalition of Social Democrats and Greens will defeat efforts by the opposition in the Upper of House of Parliament.
by Urs Geiser