Sion 2026 have claimed a National Council decision to open a vote on their Winter Olympic and Paralympic Games bid to the whole of Switzerland could "torpedo the chances" of their candidacy.
The National Council passed a motion by Swiss politician Silva Semadeni, which would give the country, not just the Canton of Valais the opportunity to vote on whether the bid should proceed.
A total of 92 votes were cast in favour of the motion, with 87 against and seven abstentions.
The National Council is the lower house of the Federal Assembly of Switzerland, with the upper house -the Council of States – now set to decide whether to support the motion.
According to 24 Heures, a Federal vote would not be able to take place until July in 2019.
Hans Stöckli, vice-president Sion 2026, has reportedly claimed it would mean their bid would have to end.
Five politicians in the Canton of Valais, in which Sion is based, have hit out at the decision and have called for the Council of States to overturn the decision.
René Constantin, Alex Schwestermann, Anton Andenmatten, Franz Ruppen and Serge Métrailler released the statement.
"While the Grand Council of Valais has just welcomed the candidacy of 2026, the decision of the National Council to submit to vote the Sion 2026 project causes our incomprehension," a joint statement read.
"We denounce an attack on the Confederal solidarity and a delaying tactic to torpedo the chances of the Valais application.
"This decision is contrary to the principles of our democracy.
"It is a way of preventing us from organisng the Olympic Games.
"We officially call on the Council of States to correct the situation.
"Valais and the Alpine regions have always supported major projects, be it Expo 2002 or Eurofoot, but now that we have to reciprocate, a majority of circumstance refuses to trust us.
"We call the Valaisans to react.
"The vote of June 10 should be a plebiscite.
"The Canton must show its determination to organise human games, sustainable and responsible.
"We also call the Valais elect to the Federal chambers to commit together to defend the Sion 2026 candidacy.
"This project is a chance not only for the Valais and the Alpine regions but for the whole country."
The Swiss Olympic Committee and Swiss Government have backed a joint proposal by Sion, the capital of canton Valais, to bid for the 2026 Games and to share it with neighbouring cantons Vaud, Bern and Fribourg.
The proposal is to use existing venues but the Swiss Government have still pledged to contribute CHF 1 billion (£720 million/$1 billion/€810 million), if it is chosen.
A referendum is due to be held in Kandersteg on June 8 and Valais on June 10 to decide whether the bid continues.
In an opinion poll published in the Le Matin Dimanche and SonntagsZeitung newspapers last month, 43 per cent of people said they were against the Sion 2026 bid and 16 per cent said were "quite against" the idea.
Only 20 per cent said they were in favour, while 16 per cent said they were "quite in favour".
There were five per cent who said they had no opinion.
Switzerland has not hosted the Winter Olympics since St Moritz in 1948.
Sion has bid three times for the Games, losing to Denver for 1976, Salt Lake City for 2002 and Turin for 2006.
If Sion does bid, it is likely to face opposition from Sapporo in Japan and Calgary in Canada.
Stockholm in Sweden and Graz and Schladming in Austria are also deciding whether to bid.