The biometric passport was approved by 50.1 percent to 49.9 percent margin, reflecting widespread concern over government intrusion into people's privacy in a country that does not belong to the European Union and has long valued its independence.

Turnout for the referendum was 38 percent, the official figures said.

Switzerland joined Europe's control-free travel zone last year, which requires countries to register citizens' facial and fingerprint images on an electronic chip in the passport.

Sunday's referendum was forced by a group of left-wing parties and junior politicians of the political left and right, who collected enough signatures to have a vote questioning the government's decision to bring its travel rules in line with European standards and the U.S. visa waiver requirement.

Lukas Reimann, 26, a member of the nationalist Swiss People's Party, said he was disappointed with the result.

Reimann _ who like many of his generation puts personal data on the social-networking site Facebook _ had said a passport with an electronic chip would be not secure and that there was no control about what foreign customs officials would do with the data.

The Social Democrats, the Green Party and campaign groups had warned the Swiss of "coercion to biometrics," and said "no against a surveillance state."

A countrywide data base collecting citizen's personal facial images and fingerprints could easily be abused by authorities for surveillance, they said.

Most of the 27 European Union members have issued biometric passports since 2006. But Switzerland has until March 2010 to put in place the new travel document, according to European law.