Lega is facing its past as a secessionist movement of the North of Italy, with deputy prime minister Matteo Salvini demanding on Monday enhanced autonomy for the northern regions of Lombardy and Veneto.

The call for enhanced autonomy of these two northern regions is opposed by the Five Star Movement (MS5). In an open letter published by Corriere della Sera, prime minister Giuseppe Conte called on the governors of the two regions to stop pushing for a reform that is unconstitutional.

The governor of Lombardy, Attilio Fontana, and Veneto, Luca Zaia, are drawing a red line over enhanced autonomy. In October 2017 the two regions voted in regional referenda for greater autonomy. At the time, the regional governor of Veneto Luca Zaia called the referenda results an institutional “big bang.”

Although Lega has made clear that northern regions do not aspire to outright secession, they are seeking a bigger share of their tax revenue. Since 2017, Lega North is a nation-wide party called Lega. However, its electoral stronghold is still the North of Italy and this has become a “do or die” issue for its national leader, Salvini.

“The government depends on the autonomy reform,” deputy prime minister Salvini said on Monday, only 14 months after the formation of a government led by MS5, whose electoral stronghold is in the South.

Lombardy and Veneto are home to around a quarter of Italy’s population and account for 30% of its economic output. As “net contributors” to the Italian budget, the regions are key to redistributive policies championed by MS5.

Lombardy sends €54bn more in taxes to Rome than it gets back in public spending; Veneto’s net contribution is €15.5bn. The two regions want to halve these contributions and want the power to develop their own infrastructure, environment, health and education policies.

If the MS5 and Lega fail to reach an agreement, Italy could go to the polls in autumn.  Almost all national papers suggest that Salvini is facing mounting pressure to bring down the coalition, with his closest advisers arguing the party’s surging popularity would see it triumph in early elections.

An opinion poll in Corriere della Sera newspaper on Saturday showed the League at 35.9%, while MS5 has seen its electoral influence halved to 17.4%.