The Sardines, an Italian movement that has emerged in response to the far-right politics of Matteo Salvini and his allies, is gearing up for a major demonstration ahead of crucial elections in the leftwing stronghold of Emilia-Romagna in late January. The movement, founded in mid-November by a group of four friends from Bologna in response to Salvini’s threat to “liberate” Emilia-Romagna from the left, has attracted a huge following, with thousands of supporters cramming into piazzas across the country in recent months.

The next show of strength is planned for Bologna next Sunday, a week before a regional election that is seen as an important test for the stability of the national government coalition between the centre-left Democratic party (PD) and the Five Star Movement (M5S). The precarious alliance came together last summer after Salvini’s League party was forced out of government following his failed attempt to force snap elections.

Support for the League has dwindled but it is still Italy’s biggest party, and winning in Emilia-Romagna would be a major coup for Salvini and his regional partners, the smaller far-right party, Brothers of Italy, and Silvio Berlusconi’s Forza Italia.

The coalition’s candidate, Lucia Borgonzoni, is polling slightly behind Stefano Bonaccini, the incumbent president from the PD. If Bonaccini manages to maintain that lead in a region where the League has galvanised support in many areas, mostly because of disillusionment with the left, then much of it would be due to the influence of the Sardines. “This is the main importance of the Sardines, to mobilise people and build the fight against Salvini,” said Massimiliano Panarari, a politics professor at Rome’s Luiss University.

The debut Sardines demonstration in Bologna attracted an estimated 15,000 people, and quickly spread across the country, culminating with a national rally in Rome in December that brought an estimated 40,000. A host of other events have taken place in smaller towns and cities.

How the movement develops will depend on the outcome of the vote in Emilia-Romagna. A meeting of national representatives is planned after the elections, leading many to believe it could become a political party, despite denials by Mattia Santori, one of the founders.

“If Salvini’s coalition wins in Emilia-Romagna, which would mean a political earthquake for the PD, then there could be the possibility of the Sardines transforming themselves into an organised structure as the PD’s failure would leave a void in the left,” said Panarari. “If the PD is able to resist, and thanks also to the Sardines’ ability to mobilise voters, I think the leaders of existing leftwing parties could invite the most prominent Sardines members to join them.”