The right-wing People's Party (SVP) is behind the Self-Determination Initiative prompting two referenda on Sunday that seek to ensure that the constitution trumps existing and future international treaties signed by Switzerland.

The SVP charges that politicians have failed to implement previous constitutional referendums on curbing migration and expelling criminal migrants by hiding behind Switzerland's pacts with the EU and the European Convention on Human Rights.

However, campaign slogans such as "Who decides Switzerland's future - international organisations and courts, or Swiss voters?" have likely failed to win support from a majority of Swiss voters, according to recent polls.

Conservatives, liberals and social democrats, who rule with the SVP in Switzerland's traditional broad coalition government, reject the proposal.

They warn that Switzerland's role as an economic hub and as a dependable diplomatic partner would be at risk if treaties that clash with the constitution were nullified.

The 5.3 million eligible Swiss voters also get to decide on a plan to subsidise farmers who let their cows and goats grow horns, rather than cutting them off.

Greens, leftists and animal welfare activists who back the Horned Cow Initiative argue that the cutting inflicts pain, and that cows with horns are healthier and happier.

Most of the other parties warn that farmers might end up tethering such animals in stables, rather than letting them walk around indoors.

Polling has shown that voters are split on the issue.

Australian Associated Press