Italy’s Lower House has passed a law that will make it increasingly difficult for anti-establishment party Five Star (M5S) to win in the country’s next round of elections.

Lawmakers approved the legislation in a “secret vote” last Thursday. It passed with a large majority — 375 yes votes versus 215 no votes — with the ruling Democratic Party (PD) and opposition parties Forza Italia and Northern League collectively throwing their weight behind it.

The “Rosatellum” law introduces a system whereby 36 percent of the seats will be allocated via a “first-pass-the-post” system and 64 percent proportionally. It also harmonizes the voting systems between the Lower and Upper Houses.

CitiGroup economist Giada Giani said the Rosatellum law “would favor mainstream parties against M5S, as they should be better in forging alliances and generally have stronger local MP candidates to win the first-pass-the-post seats.”

In an interview with CNBC last month, M5S leader Luigi di Maio ruled out the possibility of forming an alliance with other parties, saying: “We are happy to receive the support of other political parties, but we will not give them a representation in our government.”

Di Maio also criticized the then-proposed law, saying that “all Italian parties are trying to defeat us by approving an undemocratic electoral law.”

“With this law, the party that wins the election will get the least seats in parliament,” he said.

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As per current law, a party needs to obtain at least 40 percent of votes to gain the “majority premium” of another 50 seats. Average polling indications have both PD and M5S around 27 percent, while Northern League is polling 15 percent and Forza Italia, led by ex-Prime Minister Silvio Berlusconi, is polling around 14 percent.

A center-right bloc, therefore, is likely to win over M5S but is still unlikely to get an absolute majority.

The Rosatellum law will be voted on in the Upper House this week and is expected to pass and then pave the way for early elections. Local newspaper Corriere reported that President Sergio Matterella may announce the new election date as March 4, 2018 during his annual New Year’s Eve speech. That would be two months before the election date deadline of May 20.