The government is facing calls to take steps to halt the increase in the number of conscripts who choose civilian service over duty in the militia army.
In 2009, more than 7,200 men – nearly four times up on previous years - asked instead of military service to be allowed to do some form of community duty, which is 50 per cent longer.
Less than a year ago parliament suspended personal vetting procedures for conscientious objectors.
The Senate on Tuesday approved a motion in line with the House of Representatives asking the government to draft an amended law and examine the reasons for the popularity of civilian service.
Supporters warned the armed forces were at risk of losing too many of their members.
But opponents said it was too early for another reform and blamed the armed forces for shortcomings.
The government said a study was underway and the time was not right for another modification of the law.
Urs Geiser, swissinfo.ch