The referendums will take place on October 22nd, the regions announced on Friday - and although the results of the vote will not be legally binding, they could have major implications for Italy's general election next year.
At the heart of the issue is money: Grimoldi said the regions were fed up with "giving 80 billion euros [each year] to the state coffers".
"At this point the only path to get a response to the 'Lombardy question' and the 'Veneto question' is through a referendum," said Paolo Grimoldi, a key figure in the far-right Northern League said in a statement. "The time for answers from Rome has run out, as has the patience of citizens."
Lombardy and Veneto are responsible for producing respectively around 20 and ten percent of Italy's total GDP. They both pay several times more money in taxes to Rome than they receive in investment and services.
Veneto's Northern League president Luca Zaia has been a leading voice in the calls for greater regional autonomy.
Zaia had initially called for a referendum asking Venetians if they wanted to secede from Italy, or control the tax revenue collected in the northern region, but Italy's Constitutional Court blocked the plan.
Instead, Venetians will be asked if they want the region to receive "further forms and particular conditions of autonomy". The question which will be posed to Lombardy residents has not yet been decided.
The status of the regions of Italy - which only became a unified country in 1861 - is complicated. The peninsula is home to the microstate of San Marino, and the independent city-state of Vatican City, and of the 20 regions, five currently enjoy special status.
The regional councils of Sardinia, Sicily, Trentino-Alto Adige/Südtirol, Aosta Valley and Veneto's neighbour Friuli-Venezia Giulia have been granted special powers by the Italian government over their legislation and administration. It is this sort of privilege that Lombardy and Veneto are fighting for, with greater financial control the biggest issue.
But if the results won't be legally binding, what effect will they have on Italy?
According to Franco Pavoncello, a political science professor and president of Rome's John Cabot University, a strong vote in favour of autonomy would give a huge boost to the politicians fighting for a bigger share of tax income, and bring the issue of regional powers to the forefront of political debate.
"It's all about the money. [Lombardy's regional president, Roberto] Maroni said that if the state gives them more funds, he won't hold the referendum," Pavoncello told The Local.
"They aren't asking for 'independence' but administrative authority," he explained. "First they'll vote, then in the event of a 'yes', the state will need to decide how to react. There are two main ways the issue could be settled: a reform of the entire country toward a federal system, or the possibility of particular regions being given special status."
The Northern League party has long backed independence for Veneto, Lombardy, and Piedmont, supporting independence bids from other European regions such as Scotland and Catalonia.
However, a win in the October referendums could cause headaches for the party in its efforts to expand its appeal across the centre and south of the country. Party leader Matteo Salvini has officially given his support to the regional councillors in their quest for autonomy, but hasn't spoken publicly about the referendums, instead using his social media platforms to voice support for French presidential candidate Marine Le Pen.
But Pavoncello doesn't think the party will be too worried about losing some votes in the central or southern regions. "Their aim is to reinforce the two regions are the most important for their political party, and are losing votes to the Five Star Movement, for example," he explained.
Previous polls in the regions show strong support for independence.
In December, Veneto's Northern League council approved a bill defining Venetians as a "minority", allowing locals to define their nationality as Venetian and to teach the local language in school. At the time, Italian daily Repubblica dubbed the vote 'Venexit' and local councillor Riccardo Barbisan labelled it "an important step towards giving greater strength to the Veneto's request for autonomy".
In 2014, an unofficial online poll organized by the Indipendenza Veneta party - which campaigns for total secession from Italy, arguing that this is legal under international law - showed that 89 percent of Venetians favoured total independence. Two further opinion polls the same year estimated support for independence at between 51 and 54 percent.