Members of Itay’s anti-establishment Five Star Movement (M5S) are voting online on whether to support a proposed coalition with the Democratic party (PD).

The two parties unveiled a shared policy programme on Tuesday to serve as the basis of a new coalition government, putting an expansionary 2020 budget at the top of their agenda.

The traditional foes have agreed to form a new administration to head off snap elections after the previous administration comprising M5S and the far-right League collapsed last month.

About 100,000 people who subscribe to M5S’s Rousseau website had from 9am until 6pm on Tuesday to answer the question: “Do you agree that the Five Star Movement should form a government together with the Democratic party, chaired by [the prime minister] Giuseppe Conte?”

About 30,000 voted in the first two hours, according to the organisation that runs the M5S platform. A no vote would probably result in an early election.

With voting under way, the parties published a 26-point programme that would underpin the planned government. At the top of the list was a commitment to use the forthcoming budget to help stimulate economic growth, but also a promise that it would not endanger public finances.

Italy has the second-largest debt burden in the European Union as a proportion of economic output, and the pact called for greater flexibility from Brussels to overcome the “excessive rigidity” of existing budget rules.

Emphasising social justice, the two parties pledged to introduce a minimum salary, avoid a planned VAT sales rise and boost spending on education, research and welfare. The programme also called for a web tax on multinationals and the creation of a public bank to help boost development in the south.

“This is a very delicate moment for the country. It must be tackled by focusing on the interests and needs of citizens, of the community that we all form together,” M5S said in a blogpost on Tuesday, calling on its supporters to back the coalition deal.

The M5S senate whip, Stefano Patuanelli, said on Monday that if a majority of participants in the polls voted no then Conte would have to tell the president, Sergio Mattarella, that his attempt to form a government had failed. The M5S leader, Luigi Di Maio, told a meeting of his deputies that everything depended on the Rousseau vote.

M5S’s Rousseau website was launched in 2016. Photograph: Andreas Solaro/AFP/Getty Images

Web-based direct democracy has been one of M5S’s core principles since it was founded in 2009 by the comedian Beppe Grillo and Gianroberto Casaleggio, an entrepreneur who died three years ago.

In its early years, the movement used its website and Grillo’s blog to debate and hold votes before Rousseau, a purpose-built platform named after the 18th-century Swiss-born philosopher Jean-Jacques Rousseau, was developed and introduced in 2016.

But the system has been plagued by hacking attacks during key votes, and in April Italy’s data protection authority fined the company that runs the platform €50,000 (£45,000) for failing to protect users’ personal details.

M5S has held dozens of online votes on key decisions, including one to elect Di Maio and another on whether to enter its previous coalition with the League. The most recent online ballot was on whether to vote in parliament to defend the League’s leader, Matteo Salvini, from prosecution for preventing migrants disembarking from an Italian coastguard ship.

Italy was plunged into chaos last month when Salvini withdrew the League from its fractious alliance with M5S, as he sought to exploit his party’s popularity to bring about snap elections and become prime minister.

The dramatic move threatened to create a fully far-right government. But Salvini, whose tactics have dented his popularity in recent weeks, had not banked on M5S teaming up with the PD. Though the two parties are longstanding enemies, they are also the two largest parties in parliament.

If Conte fails to form a new government, Mattarella is likely to call for new elections.

The League remains the most popular party, despite toppling the government. A poll published on Saturday by Corriere della Sera showed support for the League fell to 31.8% from a mid-July record high of 35.9%. M5S rose almost seven percentage points from mid-July to 24.2%, according to the same poll, while the PD rose marginally to 22.3%.

Some M5S figures have criticised the decision to put the coalition to an online vote.

“The vote on the platform is part of the history of our movement,” said Roberta Lombardi, a former M5S parliament whip, in an interview with Fatto Quotidano. “But it doesn’t seem easy to communicate the meaning and the points of such a complex agreement in just a few days. Also because the president of the republic is in a hurry to find a solution.

“The voting on the platform is not, in this delicate moment, the most appropriate tool, given the timing,” the M5S deputy Michele Nitti wrote on Facebook. “I am surprised the decision to do so was taken, despite the concerns that emerged after the last meeting with the colleagues of the Movement.”

In a statement to the Adnkronos agency a few days ago, another M5S deputy, Flora Frate, asked Di Maio to withdraw the vote on Rousseau because “binding Mr Conte via the result of a vote on a platform run by a private company, without any guarantee of transparency, is absurd”.

Massimiliano Panarari, a politics professor at Luiss University, in Rome, said: “The vote on Rousseau is part of the M5S tradition and was presented as an example of direct democracy, even though it is far from it.

“Submitting the agreement between PD and M5S to the vote seems an affront to the institutions and to the same democratic representation, after President Mattarella formally commissioned Conte to find an agreement to form a new government.”

Reuters contributed to this report