Opinion polls ahead of the plebiscite showed around two-thirds of voters likely to reject the proposal to scrap conscription spearheaded by pacifists and backed by left-wing parties.
Switzerland's political right, parliament and cross-party government all oppose the plan, and not simply due to cliches about the army being as Swiss as its pocketknives.
Countries across Europe have ditched the draft in the two decades since the end of the Cold War, and pro-change campaigners say Switzerland should follow their lead.
Switzerland has not been attacked since the early 1800s, though the two world wars sparked mass mobilisation.
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Armed neutrality has been the bedrock of its defence policy for two centuries, with part-time soldiers keeping their arms at home, and also playing a major role in disaster relief or security at international summits.
Switzerland is ringed by friendly nations, but the pro-draft camp says a mass, part-time army is essential in a world of morphing threats -- something the referendum campaigners reject hands down.
"Compulsory military service is a tool created for wars of the past," he told AFP.