Swiss citizens are going to the polls to vote on a proposal to ban smoking completely in enclosed public places.
Hotels, restaurants and bars are currently allowed to have rooms for smokers but critics say this harms the health of those who work in them.
Restrictions introduced two years ago were watered down after lobbying from the catering trade and tobacco firms.
Opinion polls show the Swiss - who smoke more than their neighbours - are likely to reject the proposal.
The BBC's Imogen Foulkes says Switzerland is tackling the issue of passive smoking far later than its neighbours Germany, Italy and France, which long ago banned smoking in public places.
The restrictions finally introduced in Switzerland two years ago were a compromise.
Special smoking rooms were allowed in many public places following lobbying from the hotel and catering trade as well as major tobacco companies whose European headquarters are based in Switzerland.
Critics say the restrictions have also been applied unevenly across Switzerland's 26 cantons.
Eight cantons, including Geneva, have a total ban on indoor smoking in places of employment - like restaurants and bars - and public spaces - like hospitals - but the remaining 18 cantons apply the law less restrictively.
Jean-Charles Rielle, a doctor and member of the committee behind the proposal, told AFP news agency that they wanted to clear up the confusion.
"In the cantons where these laws [banning smoking rooms] are already in effect, we saw immediately... a 20% drop in hospitalisation due to cardiovascular incidents, heart attacks and these kinds of problems," he said.