The Swiss government on Tuesday urged voters to reject a referendum brought by the right-wing Swiss People's Party to end an accord with the European Union on the free movement of citizens.
Should the party win the binding vote on May 17 in what is being called Switzerland's "Brexit moment", the country could lose its privileged access to the EU single market that is the lifeblood of its economy.
It could also end up kicking Switzerland, which is not a member of the EU, out of the Schengen system of passport-free travel and the Dublin accord on asylum requests, Justice Minister Karin Keller-Sutter told a news conference in Bern.
"We would really reach a point where we would have to start from scratch in forming our ties with the EU," she said.
A rupture in bilateral ties would put Switzerland in a much tougher spot than Britain after Brexit, as the EU would have no duty to negotiate, she said.
"We would practically be a supplicant to our biggest trading partner", she said. The EU absorbed 52 percent of Swiss goods exports and generated 70 percent of Swiss imports in 2018.
The referendum drive reflects unease with the influx of foreigners who make up a quarter of the Swiss population.
Net migration from the EU and EFTA countries Iceland, Norway and Liechtenstein increased by nearly 32,000 last year, half the number in 2013, Keller-Sutter noted.
Business leaders say they need skilled foreign workers.
The eurosceptic People's Party - the biggest in parliament and with two of the seven federal cabinet seats - has long fought to take national control of immigration.
It is not uncommon for different parties in the Swiss government to pursue different policy ideologies as all important issues in the country are dealt with by referendums.
The party's proposal would allow a year to negotiate an end to free movement, but chances of this are practically nil given the EU's hard line on a policy tenet.
A "guillotine clause" means ending free movement would scupper other pillars in a web of 120 custom-made bilateral pacts, including accords on the mutual recognition of industrial standards, public procurement, agriculture, research, and transport by land and air.
The Swiss government has long struggled to revamp EU ties.
Brussels wants the Swiss to endorse a new treaty that would have Bern routinely adopt single market rules and create a more effective platform to resolve disputes.
The Swiss have dragged their feet for months while trying to forge consensus on how to proceed, annoying Brussels and triggering a row over cross-border stock trading.
The treaty ran aground amid opposition that spanned the normally pro-Europe center left to the anti-EU far right. Critics say the pact infringes Swiss sovereignty to the extent that it would never get through parliament or pass a referendum.