The leader of Italy’s anti-establishment 5-Star Movement took his campaign for a referendum on the euro to Brussels on Wednesday, holding out the prospect of cooperating with other anti-euro parties.

Beppe Grillo, the former comic who has built the 5-Star Movement into Italy’s second biggest political force, has frequently called for voters to be allowed to decide whether to stay in the eurozone.

The constitutional hurdles would make a full referendum on Italy’s membership of the single currency almost impossible to organise, but Grillo said he would press for a consultative referendum through a public petition.

“If we can take 3 or 4 million signatures into (Italy’s) parliament, then miracles can happen,” Grillo told reporters during a visit to the European parliament.

In 1989, Italians voted in a consultative referendum on the powers of the European parliament, which gave an indication of popular opinion without the full force of law.

Even if it could not change the law immediately, a similar referendum on the euro would have the potential to stir growing hostility to the single currency in Italy after six years of severe economic crisis.

The 5-Star Movement appears to have lost some of the momentum which gave it around 25 percent of the vote in last year’s parliamentary elections. But opinion polls still suggest it remains Italy’s second strongest force behind Prime Minister Matteo Renzi’s centre-left Democratic Party.

As he pressed for action, Grillo appeared to drop some of his usual hostility to rival parties, suggesting he may be prepared to work with other eurosceptic groups such as the anti-immigrant Northern League, whose leader Matteo Salvini has also called for a referendum on the euro.

“It doesn’t matter if it’s Salvini or the left or the right. We want to work on projects,” Grillo said. “If the project is good and everyone agrees, we’ll go forward with anyone.”