A year after Switzerland voted "against mass immigration", the EU is asking for a new referendum on the subject if the country wants to resume normal relations.

In an interview with Swiss newspaper La Liberte, EU diplomat Maciej Popowski said that a new referendum is "inevitable, probably at the end of 2016".

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Switzerland must "change logic", said Popowski, who is deputy secretary general of the EU diplomatic service and in charge of negotiations with the confederation.

"Rather than thinking about what they could still get, it might be useful that the Swiss see the enormous advantages they have by participating in the internal market, which they take for granted," he added.

In February 2014, Swiss voters backed a popular initiative "against mass immigration" presented by the populist Swiss People’s Party.

As a result, the Swiss government presented legislation to introduce immigration quotas in 2017, including for cross-border workers.

The confederation also wants to renegotiate its 2004 freedom of movement pact with the EU, under which it became a member of the EU's passport-free Schengen Area in 2008.

The EU has ruled out changes, however. Last December, it "reconfirm[ed] the negative reply in July 2014 to the Swiss request to renegotiate the agreement".

The EU "considers that the free movement of persons is a fundamental pillar of EU policy and that the internal market and its four freedoms are indivisible," EU ministers said in a statement in December 2014.

Agreements in other sectors, such as the electricity market or integration of Switzerland into the EU financial services market, also depend Swiss compliance, Popowski told La Liberte.

"No lasting agreement will be signed before institutional issues are settled. And no definitive agreement will be reached before the problem of free circulation is solved," he added.