Speaking to Swiss tabloid Blick, SVP party president Albert Rösti said 125,000 signatures had been collected for the anti-freedom of movement initiative.

These will now need to be officially verified before the initiative is submitted, expected to be in September.

Under Swiss law, any group of at least seven citizens that collects 100,000 signatures within 18 months can demand a change to the constitution via referendum.

Read also: Swiss-EU deal – Bern may back down over controls on foreign workers

If the SVP referendum does go ahead and receives the backing of the Swiss people, it would mean EU citizens would no longer have the automatic right to work in Switzerland.

Rösti said freedom of movement “is damaging to prosperity [in Switzerland] in the long run” and denied that scrapping the freedom of movement deal with the EU would cause major damage to relations with Brussels.

The comments from the SVP chief ramp up the pressure on the Swiss government, coming as they do on the same day that Swiss Foreign Minister Ignazio Cassis is expected to unveil a new deal designed to break the deadlock in stalled talks between Bern and Brussels on a new framework agreement regarding their bilateral arrangements.

Tensions between the Bern and the Brussels date back to 2014 when Swiss voters backed another SVP-powered referendum – the ‘against mass immigration' initiative –which aimed to impose limits on immigration from EU countries and therefore protect the rights, and high incomes, of Swiss workers.

Aware that implementing the measures restricting EU freedom of movement contained in the referendum text could seriously threaten Swiss access to the European Common Market, the Swiss parliament finally approved a watered-down version of the initiative.

This involved imposing new rules on unemployment which should limit the impact of foreign workers on the domestic job market.

But the parliament’s decision to pass a “lite” version of the mass immigration initiative angered the SVP while it failed to fully satisfy Brussels over the issue of access of EU workers to the Swiss job market.

Under the new deal expected to be proposed by the foreign minister to the Swiss government on Wednesday, Bern would make concessions to the EU by tweaking its eight-day rule which requires foreign companies to inform Swiss authorities at least eight days before they carry out work in Switzerland so that the Swiss can ensure firms are not bringing in cheaper labour to undercut high wages in the Alpine country.

In exchange, Brussels would accept a more limited role for the European Court of Justice (ECJ) in Swiss affairs.