The Federal Court is set to rule on a challenge to the narrow approval of the Swiss e-ID law.
The measure passed with just 50.4 percent of the vote last September.
Opponents argue the result was skewed by support from state-linked Swisscom and undisclosed media backing, and are calling for the vote to be annulled.
The case now sits before the Federal Supreme Court of Switzerland, which will hold a public hearing tomorrow.
If judges side with the complainants, the referendum could be rerun.
If that happens it will be highly unusual - the court has ordered a federal vote to be rerun only once since 1848 - in 2019 it decided the ‘for marriage and family’ initiative needed to be held again after the federal council had provided incorrect information to the voters.
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