The measure had been expected to fail, but the debate has tapped into a vein of discontent among Swiss voters who in March backed rules to rein in golden handshakes, in the wake of high-profile exit payments to top bosses.

Dubbed the “1:12” initiative after the legally-binding ratio it would set between the top and bottom salaries in a firm, the plan met with stiff opposition from Switzerland’s business community and political right.

Ahead of the vote, its critics issued stark warnings that inscribing salary restrictions into the law would make the wealthy Alpine nation less competitive and break with a Swiss tradition of limited official meddling in business.

“There’s a climate of mistrust towards those who make money,” Jean-Claude Biver, boss of high-end watchmaker Hublot, told the Swiss daily Le Temps.

Christoph Darbellay, head of the centre-right Christian Democratic Party, told AFP he could understand disquiet over “undeserved salaries”.

But voting Yes would be tantamount to “shooting ourselves in the foot”, he insisted.

Switzerland’s cross-party government had urged a No vote, saying a 1:12 law would dent tax revenues and scare off foreign firms.

Switzerland, which has long boasted a business-friendly climate coupled with one of the highest average salaries in the world, has largely avoided the economic crisis dogging the European Union, of which it is a staunch non-member.

The referendum campaign was spearheaded by the Socialist Party, plus the Greens and trade unions.

They rejected the criticism, arguing that it was time to clip the wings of the vastly overpaid, and underlining that an informal ratio of around 1:12 was the norm as late as 1998, before things went awry.

Under the direct democracy which is the core of the Swiss political system, the campaigners were able to put the issue to a plebiscite by collecting more than 100,000 signatures.

The debate led to intense scrutiny of bosses’ pay packets, which the 1:12 proponents said were an average 43 times higher in 2011 than those on the bottom of the ladder.

According to 2012 figures published by the campaigners, the then boss of pharmaceutical giant Novartis made 219 times the lowest salary.

At banking group UBS, the lowest-paid employee would have had to work 194 years to make the same amount the head of its investment bank raked in 12 months.

The chief executive of rival bank Credit Suisse enjoyed a ratio of 1:191.

And at insurer Swiss Life — whose chief is also treasurer of the Economie Suisse trade and industry lobby — it was 1:60.

To hammer their message home, the campaigners plastered Switzerland with posters showing a single hamburger next to a towering stack of a dozen, reading: “12 times more salary, that’s enough”.