Switzerland will also hold votes on May 18 on a multi-billion-dollar deal to buy fighter jets from Sweden, which is on a knife-edge and measures to ban paedophiles from working with children, which is almost certain to pass.
Much of the national debate ahead of the referendum, which are held every three months in Switzerland as part of the country's direct democratic system, has focused on the pros and cons of introducing a minimum wage.
The unions and left wing political parties behind the "Decent Salary" initiative insist at least 22 Swiss francs (25 USD) an hour or 4,515 USD a month, is needed to survive in Switzerland, one of the world's most expensive countries.
If the voters agree, the wealthy Alpine nation would go from having no minimum wage to boasting the world's highest, far above the 7.25 USD in the United States, 9.43 euros in France, 5.05 euros in Spain and the recently agreed 8 euros in Germany, set to take effect next year.
According to the latest poll published last week, a full 64 per cent of Swiss voters oppose the initiative, with only 30 per cent supporting it.
They have warned a minimum wage, and especially such a high one, would be a death blow to many businesses and would weaken Switzerland's healthy economy.
Supporters of the initiative counter that higher basic wages would boost the purchasing power of some 330,000 people.
People working in sales and services and farming, or as hairdressers and flight attendants, for instance, generally earn well below 4,500 USD a month.
The government and other supporters have meanwhile been campaigning hard to stress the importance of the new planes for Swiss security, and observers say the scale could still tip in their favour.
There is little suspense around the third referendum, which calls for convicted paedophiles to be automatically banned for life from working with children.
A poll last month hinted 74 per cent of voters welcomed the initiative despite opposition from the government and most centre-left parties, who deem it is too stringent and superfluous, since Swiss law already makes such bans possible.