The climate fund initiative, launched by the Social Democratic Party and the Greens, calls for the country to spend 0.5-1.0 percent of Switzerland's annual GDP -- around 4-8 billion Swiss francs ($5-10 billion) -- on fighting climate change.

It will be voted on Sunday. Under Switzerland's direct democracy system, 100,000 signatures are needed to put virtually any issue to a popular vote, with the Swiss given a say on a wide range of topics every few months at the national, regional and local levels.

Backers of the climate fund initiative insist it is needed "to support the reduction of greenhouse gas emissions, the economic and efficient use of energy, and the development of renewable energies".

While this would mean at least doubling the amount Switzerland currently spends on climate protection, the Socialists and Greens argue that the cost of inaction would be far higher.

"Today, we spend eight billion a year abroad in more or less autocratic countries to import fossil fuels," Green Party chief Lisa Mazzone recently told Swiss public broadcaster RTS.

She argued that "a climate fund would not only accelerate the transition (to renewable energy), but also create jobs and keep added value within the country".

- 'Too heavy a burden' -

But the Swiss government and parliament have urged voters to reject the initiative on Sunday.

They argued it would be far too expensive, and highlighted that the country currently spends around two billion francs a year -- from a budget of around 90 billion francs -- on climate protection.

Such a fund would "place too heavy a burden on federal finances", they warned.

Recent opinion polls indicate that most voters agree.

Pollsters gfs.bern showed that 52 percent firmly opposed the initiative, while the latest Tamedia/Leewas poll put the figure at 62 percent.

Polls meanwhile suggest that voters might embrace another issue on the ballot Sunday: an initiative calling for enshrining in the constitution a guarantee of maintaining cash payments with coins and banknotes.

And there was suspense around whether a referendum would pass on a federal tax reform to tax the income of married couples separately.

It meanwhile appeared clear that the final issue on the ballot -- an initiative calling for dramatically slashing Switzerland's media licence fee to 200 francs per year from 335 francs currently -- would not pass.

The government has urged voters to reject the initiative, put forward by a committee made up of members right-wing parties and the Swiss Trade Association.

The higher fee, it insists, is needed to "guarantee public service in all linguistic regions" of the country, which has four official languages: German, French, Italian and Romansh.