European partners have threatened to review their relations with Switzerland after voters in the Alpine nation narrowly backed a proposal to curtail immigration from the EU in a referendum.
French Foreign Minister Laurent Fabius described the vote on Monday, initiated by the right-wing Swiss People's Party (SVP) and opposed by the government in Berne, as a "worrying" move that showed Switzerland was withdrawing into itself.
"We're going to review our relations with Switzerland," Fabius told RTL radio. He added that the EU's agreement with Switzerland has a "guillotine clause" that means if one element is challeged, "then everything falls apart".
The vote was met with an averse response from EU leaders.
Luxembourg's Foreign Minister Jean Asselborn said "one of the achievements of the EU is the free movement of people and that can't be watered down.''
He said that if Switzerland does not honour that, it could lose its easy access to the world's biggest market.
Switzerland is not a member of the 28-nation EU, but a pact with Brussels has ensured the free movement of citizens to and from the bloc since 2002.
Sunday's vote to reintroduce immigration quotas, backed by a razor-thin margin of 19,526 voters, threatened that pact, and with it a key pillar of the Swiss economy, which relies on the EU for nearly one-fifth of its workforce.
Chancellor Angela Merkel's spokesman said that while Berlin respected the result, it would create "considerable problems" for Switzerland's relationship with the EU. The European Commission said it went against the principle of free movement between the Alpine nation and the EU that has existed for over a decade.
"The EU will examine the implications of this initiative on EU-Swiss relations as a whole," the Commission said.
The vote has raised concern about the impact it will have on Swiss businesses and banks, who are dependent on the flow of foreign workers.
Although the Swiss government had urged voters to reject the introduction of EU immigration quotas, it is now obliged to write the results of the referendum into law. It will have a degree of flexibility as the referendum did not set specific quotas.
Swiss Justice Minister Simonetta Sommaruga said on Sunday that the government planned to draft a law by the autumn, before approaching the EU with its plans.
Anger among parties that had opposed the vote was palpable on Monday, with the Swiss Liberal Democrats suggesting that Christoph Blocher, the billionaire industrialist and SVP lawmaker, be sent to Brussels himself to explain the vote.
"He has an obligation to find a good solution, together with the other parties," the FDP said in a statement.