ZURICH—Swiss voters overwhelmingly rejected an initiative on Sunday that would have forced the country’s central bank to hold one-fifth of its assets in gold, a move that would have eroded its ability to conduct monetary policy.

Citing projections from results in 19 of the country’s 26 cantons, Swiss television said roughly 78% of voters opposed the initiative, dubbed “Save Our Swiss Gold.” The gold initiative would have also barred the Swiss National Bank from selling gold in the future.

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