The Senate has rejected a proposal to abolish the compulsory construction of emergency shelters for private home owners.
Opponents, notably from the centre-right Christian Democratic Party, warned of unforeseen risks that made such protected rooms necessary and cautioned against wasting millions of francs in investment.
Defence Minister Ueli Maurer said an increasing number of countries were producing nuclear weapons.
An estimated 8.6 million people in Switzerland could be housed temporarily in shelters which cost around SFr12 billion ($14.1 billion), according to the government.
Switzerland’s system of emergency shelters was launched in the Cold War era of the 1960s amid fears of a nuclear bomb explosion.
Supporters of a reform on Tuesday said the concept of fall-out shelters was outdated and underground refuges could not provide protection.
In March – two days before the nuclear accident in Japan – the other parliamentary chamber, the House of Representatives, came out in favour of lifting an obligation for private fall-out shelters.
Discussions will continue in the House at a later date.
swissinfo.ch and agencies