A Swiss political party that successfully campaigned for a ban on building new minarets started collecting signatures on Tuesday for a referendum initiative to limit the number of immigrants to Switzerland.

The right-wing Swiss People's Party (SVP), expected to remain the biggest party in parliament's lower house at national polls in October, wants to amend the constitution to set annual quotas to limit residency permits granted to foreigners.

"With our popular initiative the SVP wants to stop mass immigration and win back control over those entering the country," the party said on its website.

Although not a member of the European Union, Switzerland has no limit on the number of citizens of the 27-nation bloc taking up employment. The SVP measure would bring the Alpine state into conflict with its treaty obligations with the EU.

Foreigners make up a fifth of the 7.7 million population and the SVP has blamed immigration, much of which comes from the EU, for pushing up rents, causing unemployment, overcrowding public transport and eroding cultural values.

SVP party delegates voted unanimously to launch the initiative at its party conference at the end of May. The party has 18 months to collect 100,000 valid signatures needed to take the initiative to a public vote.

Asylum seekers and workers who commute across the border should also be included in the quotas, while the entitlement to permanent residency, permits for partners and children and social benefits should be limited, the SVP said.

The party has also said Switzerland should reintroduce border controls to limit immigration and possibly pull out of the Schengen treaty that allows free movement in Europe.

Switzerland has the world's longest tradition of direct democracy and Swiss citizens can vote on dozens of local or state issues each year and in up to four national referendums.

Swiss voters backed SVP proposals in referendums to automatically expel immigrants convicted of serious crimes and to ban the building of new minarets.