The EU would not renegotiate its bilateral agreements with Switzerland should Swiss voters restrict immigration, a European Commission official has warned.

EC Vice President Viviane Reding said in an interview published by the Switzerland on Sunday newspaper "it is illusion" to believe the country could renegotiate its agreement with the European Union on the free movement of peoples without affecting others granting it vital access to Europe's internal market.

The remarks came in the run-up to a Feb. 9 plebiscite under Switzerland's direct democracy system sponsored by the right-wing Swiss People's Party seeking to end "mass migration" and reimpose a strict quota system limiting immigrants from EU countries.

Reding warned member nations would reject any attempt to alter Switzerland's obligations to allow fundamental freedom of movement without also jeopardizing the dozens of other bilateral agreement it has with the EU, including those governing its access to the European economy.

"It is an illusion to think that the freedom of movement could be renegotiated individually," she told the newspaper. "The free movement of persons is part of the internal market, it's part of the package. Switzerland cannot cherry-pick here or there."

If Switzerland wants changes to the movement of persons, it could only come as part of a global negotiation on its series of 120 bilateral agreements with the EU because of a "guillotine clause" that links them together, she said.

Such negotiations would "not be in Switzerland's interest," Reding said. "Switzerland is an important partner to the EU. But the EU is also an indispensable partner for Switzerland. So you should think twice about what you are doing."

At the end of 2012 there were 1.87 million foreigners living in Switzerland, nearly 23.3 percent of a total population that has surpassed 8 million. In addition, more than 270,000 cross-border workers hold a job in Switzerland, government statistics indicate.

The Feb. 9 referendum was organized by the Swiss People's Party, SVP, which blames immigrants from Eastern European nations for a series of social ills, including loss of valuable agricultural land, crowded public transportation, pressure on wages, crime, asylum abuse and the "loss of cultural identity."

It seeks to reimpose a quota -- lifted in 2011 -- of 2,000 residency permits per year for citizens of the so-called "A8" nations, which joined the EU in 2004, the BBC reported.

It will be followed by two more plebiscites on immigration set to take place before the next federal parliamentary elections in 2015. One will be on the question of whether to extend the free movement of persons to Croatia, which joined the EU last year.

The other is an initiative of the environmentalist group Ecopop aiming to protect the environment and natural resources by limiting immigration to 0.2 percent of annual population growth.

Reding said the fears of long-term consequences of immigration to the Swiss social system are unfounded, noting that only 3.7 percent of EU citizens in the country are receiving social assistance, compared with 4 percent of native Swiss.

She also asserted free movement is a two-way street -- about 430,000 Swiss citizens live in the EU.

"Without the single European market, Switzerland could hardly function," she said. "Sixty percent of Swiss exports come under the bilateral agreements to access the single market."