Neither initiative is expected to pass, according to recent polls, but they have generated significant discussion in the wealthy Alpine nation.

Under Switzerland's direct democratic 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.

The Swiss government and parliament have urged voters to reject the two national items on Sunday's ballot, arguing that they would entail huge costs and could threaten the economy.

Polling stations were to open for a few hours on Sunday morning before closing at noon (1100 GMT).

But most votes are typically cast in advance, with initial results expected by mid-afternoon.

- 'True equality' -

The so-called Civic Duty initiative initially garnered quite broad backing, but its support has crumbled in recent weeks, with the latest survey from market researcher gfs.bern finding that 64 percent of those polled were opposed.

The committee behind the initiative maintains that requiring every Swiss citizen, regardless of gender, to do national service in the army or in a civilian capacity would strengthen social cohesion.

The initiative aims for "true equality", committee head Noemie Roten told AFP.

She described the current system as discriminatory -- for men, but also for women, who are largely excluded from useful networks and experiences obtained during service.

"Be it in the army, civil protection, civil service or voluntary firefighters, the idea is for every young person to contribute to the collective wellbeing," she said.

Opponents of the initiative denied it would enhance equality.

Cyrielle Huguenot, head of equality, family and migration issues at the Swiss Trade Union Federation (USS), argued that the initiative "completely obscures the reality of women in this country".

Women already do the vast majority of unpaid tasks in Swiss society, she told AFP.

"And now you are asking women to provide even more unpaid service. This would only exacerbate the imbalance."

- 'Tax the rich' -

The second item on the ballot Sunday, known as the "initiative for a future", has also sparked controversy with its demand for a new climate tax on big inheritances.

It appears even less likely to pass, with a full 68 percent of those questioned for the latest gfs.bern poll against.

The text, put forward by the youth wing of Switzerland's Socialist Party, calls for a 50-percent inheritance tax on fortunes above 50 million Swiss francs ($63 million) -- estimated to affect some 2,500 households.

Under the slogan "tax the rich, save the climate", the group calculates that the levy would rake in six billion Swiss francs annually, which could go towards funding an ecological transformation of Switzerland's economy through things like renovating buildings, developing renewable energy and expanding public transportation.

A massive opposition campaign has warned that very wealthy people might leave the country to avoid the tax, weakening the economy.

People inheriting family businesses might also be hurt, critics caution.