ZURICH (REUTERS) - A majority of Swiss voters are against the purchase of 22 Gripen fighter jets from Swedish defence firm Saab, a poll showed on Sunday, raising the possibility that a popular vote due in May could scupper the US$3.4 billion (S$4.3 billion) deal.

Around 62 per cent of voters would reject the proposal to replace Switzerland's ageing fleet of Northrop F-5 Tiger fighters with the Gripen jets, according the survey conducted by polling institute Leger and published in Swiss newspaper SonntagsBlick.

The poll, which questioned more than 1,000 people, showed 32 per cent of those who planned to vote were in favour of the deal.

The Gripens are unpopular with some in Switzerland, which has not fought an international war for 200 years, because the deal will require cost cuts in other areas, such as education.

Switzerland's upper and lower houses voted in favour of the purchase of the jets in September, but Swiss interest groups can secure referendums on new laws if they collect a sufficient number of signatures.

The vote on the jet purchase is scheduled for May 18, the same day as a popular vote on whether to adopt the world's highest minimum wage.

The poll showed 52 per cent of voters were in favour of introducing a minimum wage of 22 Swiss francs (S$31.90) an hour, or 4,000 francs a month.

Around 42 per cent of voters said they would reject the initiative, which the government said last month would hurt competitiveness and lead to job cuts.

Swiss voters generally have a history of rejecting proposals that they feel could hurt the economy.

However, last month they unexpectedly backed a proposal to cap immigration from the European Union, despite warnings from the business and political elite that it could be detrimental to the economy.