Justice Minister Eveline Widmer-Schlumpf has signed a revised repatriation agreement with Bulgaria during a two-visit to the country.
The accord will make it easier for both governments to repatriate people, and allows Switzerland to return to Bulgaria third-country nationals who transit the Balkan state.
The justice ministry said the accord matches those Switzerland has with other European Union member states.
Bulgaria and Romania became EU members at the beginning of January 2007.
Widmer-Schlumpf said she was confident the Swiss electorate would choose to extend the Swiss-EU free movement of people treaty to Romania and Bulgaria when the issue comes to a nationwide vote in February 2009.
Together with the Bulgarian interior minister, Mihail Mikov, Widmer-Schlumpf called for closer cooperation between the law enforcement authorities in both countries to combat human trafficking.
Widmer-Schlumpf said Switzerland was not "indifferent to the exploitation of Bulgarian women".