Polls have closed following Sunday's vote on the introduction of electronic passports and a central fingerprint register.
The controversial new travel document would include the holder's electronic photograph and two fingerprints. Polls have predicted the result will be close, and first trends on Sunday confirmed that.
The vote came about after a broad political coalition challenged parliament's decision to adopt the new passport - in line with the European Union - and set up a fingerprint register.
Opponents argue that the inclusion of biometric data poses a threat to the individual's security and privacy.
Supporters for their part claim the new passports would be forgery proof, ease freedom of travel and comply with international obligations.
Pollsters found no side had a clear majority a few weeks ahead of the vote, and are predicting a below-average turnout.
Members of the European single border area, including Switzerland, are required to introduce new biometric passports by next March. The travel document should also allow visa-free entry into the United States.
Centre-left politicians have dismissed government assurances that the data would not be used in criminal investigations.
"The private sphere has to be respected, citizens must not be treated like criminals," cautioned Social Democratic parliamentarian Carlo Sommaruga.
Daniel Vischer of the Green Party criticised the Swiss government for its "pre-emptive obedience", saying only very few countries were setting up a central fingerprint register.
The Social Democrats and Greens have the backing of the rightwing Swiss People's Party as well as the youth chapters of other political groups.
Data protection officials and information security specialists have also warned of abuse by hackers and the illegitimate use of data by police and other state agencies.
"I understand the doubts and mistrust towards the state. There is plenty of evidence in the recent past of regulations being violated or changed," said Peter Heinzmann, a professor at the Rapperswil Technical College.
Opponents on the right warned that the new travel document could enable the state to interfere in the private sphere of citizens.
Justice Minister Eveline Widmer-Schlumpf who led the "yes" campaign, argued electronic passports were a way to prevent abuse.
"It will become more difficult to use someone else's stolen passport," she said.
The minister claims the new travel document is sufficiently protected against forgery and abuse and the central fingerprint database will help speed up passport procedures.
Switzerland has issued 3.9 million passports since 2003. Some 13,000 are reported lost every year.
The government also pointed out that the electronic passport would help ensure travel freedom for Swiss citizens.
The main centre-right political parties as well as the Swiss expatriate community have echoed Widmer-Schlumpf's statements and accused opponents of scaremongering.
The Swiss Business Federation and the tourism industry highlighted the importance of passports complying with international standards.
Business representatives warned that a rejection by voters would harm the key export industry and could discourage non-European tourists from visiting Switzerland.
Claude Longchamp of the gfs.berne polling and research institute said ahead of the vote the debate over data abuse had failed to strike a chord with the general public.
"The decisive factor in the vote will be whether concerns about travel restrictions or fears of state surveillance gain the upper hand," Longchamp said.
Urs Geiser, swissinfo.ch
Some 4.9 million Swiss are eligible to vote on Sunday, including 120,000 registered Swiss expatriates.
As a rule nationwide ballots take place four times a year.
In February Swiss voters approved the continuation and extension of a key labour accord with the EU.
Besides the ballot on electronic passports voters also have the final say on a proposal demanding the promotion of alternative medicines (see above).
Votes also take place in 15 of the country's 26 cantons on issues including tax, education, transport, justice, a smoking ban as well as the right to vote for 16-year olds.
The city of Zurich will decide on a SFr200 million credit for wind energy, while a culture centre, including artists' workshops, is the subject of a local vote in the capital, Bern.
Complementary medicine vote
The proposal seeks to promote alternative medicines, including traditional Chinese medicine, homeopathy, herbal and neural therapies.
Incomplete results on Sunday showed the proposal would pass, with approximately 67% of the vote.
Supporters argue such forms of treatment should be covered by the compulsory health insurance.
Opponents say including these forms of treatment would put more financial strain on the health system.
Most political parties, except for the rightwing Swiss People's Party, supported the proposal.
The government also recommended a yes vote but says alternative treatments must be effective, reasonably priced and appropriate to be included in the list of paid health services.
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