Looks like it’s back to the drawing board for Switzerland’s plan to forge a treaty with the European Union. The country’s labour unions are against it, and now the pro-Europe centre left has joined the far-right in rejecting the deal.

For the SGB union federation allied with the centre-left Social Democrats (SP), the government’s efforts to explore tweaking Switzerland’s strict rules that protect Europe’s highest wages were a step too far towards the treaty demands of Brussels.

As reported by the Reuters news agency, the far-right Swiss People’s Party (SVP) also opposes the proposals that it sees as infringing Swiss sovereignty. So political support for an accord — lukewarm to start with — now appears so low as to spell the treaty’s doom. The SVP is the largest party in the Swiss parliament and the SP is second.

Ties between the EU and non-member Switzerland are now governed by more than 100 separate agreements. Brussels wants to supersede them with a single treaty, to provide a better platform to settle disputes and to ensure that Switzerland adopts changes to the rules of the single market.

Failure to strike a deal after years of talks would plunge ties into a new ice age and could prompt punitive steps.

Swiss Economy Minister Johann Schneider-Ammann, from the centre-right Liberals, pledged to continue talks with labour, employers and Switzerland’s 26 regional cantons, in the hope of presenting joint proposals to the cabinet next month.

“A treaty seems further away than ever,” said Gerhard Pfister, head of the center-right Christian People’s Party in the four-party government coalition.

Back in Brussels, a European Commission spokeswoman said the trade union discussions were a Swiss internal affair.

“We remain ready to continue the negotiations in good faith and it will not be easy to reach an agreement. For the EU it is, however, very clear that those who want to do business in our internal market need to comply with the rules,” she said.