The measure, approved by the National Council, or lower house, calls for the introduction of obligatory referenda on any international treaties that would alter the constitution, according to the Tages Anzeiger newspaper.
Today, both the Swiss people and the cantons have to approve moves to join supranational organizations such as the European Union, but the new initiative extends the obligation to consult citizens over other treaties.
The proposal will now have to be discussed by the upper house, the Council of States, and then voted on by the people at a later stage.
The initiative was as a counter-measure to a more far-reaching proposal presented by a right-wing organization, the Campaign for an Independent and Neutral Switzerland (Cins), which failed to win a majority.
The group was calling for a law to hold mandatory referenda to rule on the approval of every international treaty. Supporters say the measure would increase international integration and extend direct democracy, a pillar of Swiss culture and history.
Those who have opposed it have said it is not realistic to ask the Swiss people to vote on every significant treaty. Votes in Switzerland can be forced on any legislation, provided enough signatures are collected.