The rightwing Swiss People's Party has by a wafer-thin majority succeeded in forcing a vote on the controversial issue of citizenship.
After two recounts and the removal of 2,300 names, the federal authorities confirmed that the party had collected enough signatures to put the issue to a nationwide ballot.
The People's Party announced in November that it had collected more than the required 100,000 signatures for its people's initiative "for democratic naturalisations".
The government said a total of 102,326 signatures had been handed in to the Federal Chancellery, but the six-man checking group judged some 2,300 of these to be invalid, leaving just 100,038 - the lowest number on record for a valid initiative.
The above-average number of invalid signatures is due to a large number of multiple votes, according to Hans-Urs Wili, head of the political rights section of the Federal Chancellery.
Around 1,000 multiple votes were weeded out and around a dozen people voted five or six times.
Wili said he would call on the authorities to instigate criminal proceedings against these people, who are under suspicion of vote-rigging, which is punishable by prison or a fine.
But Georg Lutz, a political scientist at Bern University, told swissinfo that proving fraudulent intent is easier said than done.
"If the same person signs a form more than once, that doesn't mean they did it with a view to rig the system," he said. "Collecting signatures for an initiative takes 18 months and it's possible that someone isn't sure whether they've already signed it or not."
Despite the slim margin, Lutz says the number of votes has no effect on an initiative's chances of success.
"Think of the initiative against acquiring F-18 jetfighters. Over 200,000 signatures were soon collected but the initiative was still rejected at the ballot box."
Only 15 people's initiatives have been accepted in modern Swiss history, but more than 70 registered proposals failed to clear the first hurdle because they lacked the necessary number of signatures.
The latest validated initiative is aimed at enshrining in the constitution the right of voters to decide on naturalisation requests.
The People's Party wants communities to be free to decide on how best to proceed on citizenship questions and is against allowing appeals against negative decisions.
The party's proposal challenges a 2003 Federal Court ruling on Switzerland's citizenship procedure, which effectively meant that citizenship requests could not be decided at the ballot box, by local parliaments or other assemblies.
The judges said failed candidates had to be given a reason for their rejection, to avoid arbitrary decisions.
Voters in the town of Emmen near Lucerne had, for example, turned down applicants from the Balkans, apparently only on the basis of their nationality. This pattern was repeated in other parts of central Switzerland.
A similar attempt by the People's Party to give cantons and local authorities full authority in granting Swiss citizenship was turned down by parliament in October.
Voters have generally been against easing citizenship rules in recent years, and could toe the People's Party line, say observers.
In 2004, they rejected a simplified naturalisation procedure for young foreigners for the second time in a decade.
Citizenship applicants must win approval from three different bodies, including their local authority.
Switzerland has one of the lowest levels of naturalisation in Europe.
Foreigners currently number 1.5 million – just over 20 per cent of the population.
swissinfo with agencies
If a Swiss citizen or a group of citizens can collect and hand in to the Federal Chancellery at least 100,000 signatures in favour of the amendment within 18 months, this "people's initiative" must be put to a nationwide vote.
After the cabinet and parliament have discussed it – which can take several years – the initiative goes forward to a popular vote.
Only 15 people's initiatives in modern Swiss history have been accepted at the ballot box.
More than 70 initiatives failed to get the necessary number of signatures for a vote.
About 150 initiatives were rejected by voters, others were withdrawn or declared invalid.
In 2003, the Federal Court ruled that a rejected application for citizenship must be justified.
This decision effectively banned local votes on naturalisation procedures.
In parliament, two proposals on giving local authorities more autonomy on this issue have been discussed.
The Swiss People's Party has forced – by only 38 signatures – a nationwide ballot to grant voters more of a say on citizenship procedures.
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