By Andrew Morse 

ZURICH--The head of the Swiss National Bank reiterated concerns that a popular vote on requiring the central bank to keep a fifth of its assets in gold would hinder its ability to conduct monetary policy.

In text of a speech to be delivered Sunday, SNB Chairman Thomas Jordan said the initiative, known as "Save Our Swiss Gold," would limit the central bank's "room for maneuver." That would make it harder for the bank to intervene during crises and fulfill its mandate of price stability.

"The initiative is both unnecessary and dangerous," Mr. Jordan said in the speech. "It is unnecessary because, under the current monetary order, there is no link between price stability and the share of gold in the SNB balance sheet."

On Nov. 30, Switzerland will vote on whether the SNB should be required to maintain a minimum of 20% of its assets in gold. If passed, the initiative would also prevent the SNB from selling gold and force it to repatriate its holdings of the precious metal maintained in the U.K. and Canada.

Analysts and traders believe the initiative could challenge the SNB's commitment to a three-year-old cap of 1.20 Swiss francs per euro. Such speculation has already pushed the franc to its highest level in more than two years. Gold prices have also been affected by the prospects of the vote; last week gold fell more than 1.5% after a poll showed Swiss voters were unlikely to approve the measure.

The organizers of the initiative, members of the right-wing Swiss People's Party, say the measures are needed because the SNB's policy of capping the value of the franc has left its balance sheet stuffed with euros. Those euros, they say, have been devalued in the wake of the financial crisis.

In the speech, Mr. Jordan said Switzerland's stock of gold is high compared with the rest of the world and that the SNB has no plans to sell or purchase gold.

Write to Andrew Morse at andrew.morse@wsj.com

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