In Switzerland's system of direct democracy, any voter can trigger a referendum by collecting 100,000 signatures within 18 months.

Environmentalist group Ecopop has proposed capping the number of immigrants at just 16,000 people per year, saying it is concerned about a lack of living space exerting too much pressure on the land and natural resources, rather than by opposition to foreigners.

Free movement of people is one of the fundamental policies of the EU, and Switzerland, while not a member of the 28-nation bloc, has to uphold that principle in order to benefit from favourable trade conditions.