A plan to reimpose immigration quotas in Switzerland and give existing residents an advantage in the job market could pass in a plebiscite next February, an opinion poll shows.
The highest numbers of recent immigrants come from Portugal, Kosovo, Germany, Italy and France.
Switzerland is not a member of the European Union but has tight economic ties with the 28-nation bloc.
The referendum proposal calls for the quotas to be reimposed, raising the spectre of a clash with Brussels because it sets a three-year deadline for the rules to be renegotiated.
It would also set quotas for people who live in neighbouring France, Germany, Italy and Austria but work in Switzerland.
Cross-border workers are a hot topic after recent local elections saw major gains for the Geneva Citizens' Movement, a party that claims they take jobs from Swiss residents.
The proposal also calls for the constitution to state clearly that immigration must serve the country's economic interests and guarantee the Swiss priority on the labour market.
Over and above the quotas, it stipulates that would-be immigrants must have a job offer, sufficient financial resources to get by, and be willing and able to fit in to Swiss society.
The quotas would also apply to asylum seekers.
A vote is also due by 2015 on a separate proposal by campaigners who say immigration limits are needed to rein in overpopulation and protect the environment.