Parliament has decided to tighten the rules of citizenship to prevent the misuse of immigration benefits through fraudulent marriages.
The Senate on Tuesday followed the House of Representatives in extending from five to eight years the period in which a citizenship permit can be revoked if the beneficiary turns out to have misled the authorities.
The centre-left Social Democrats and the Greens argued the amendment unfairly punished the majority of applicants.
Justice Minister Eveline Widmer-Schlumpf came out in favour of tougher regulations, saying it was often impossible to prove fraud allegations within the current statute of limitations.
The Federal Migration Office investigates about 500 suspected sham marriages every year.
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