"I can not imagine a Europe without Italy or Italy without Europe", Moscovici said.
The letter stated that Italy's budget proposal, which was initially announced in September was in contravention of the EU's budget regulations.
Tria for his part said Italy and Brussels had "different evaluations" of the situation, but added that he too looked forward to "a constructive dialogue".
Three diplomats told the Reuters news agency that Italy is also resisting European Union proposals to impose sanctions on countries that carry out cyberattacks, in another move seen as being in favour of Moscow.
While Italy's deficit is well within the 3 percent limit laid out in treaties, the commission has demanded smaller gaps for Italy to bring down its debt load, the largest in Europe in absolute terms and second only to Greece's as a percentage of the economy.
The government's budget plan targets a decrease of the deficit to 2.1 per cent in 2020 and 1.8 per cent in 2021.
Conte, in a post on Facebook Thursday, said that the measures are "well-considered, well-constructed and well-realized", and he said the draft was "the only instrument that we have to ensure economic growth and social development to our country".
"We [the commission] were very kind, gentle, and positive, when it came to Italy, because Italy is Italy", Juncker said, adding that in the last three years Rome was able to €30bn more without sanctions by the EU's stability rules.
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The 5-Star Movement leader, Luigi Di Maio, insists that the draft contains unauthorized changes to extend a tax amnesty to Italians with bank accounts overseas.
Both parties want to maintain their populist government at least until the European Parliament elections in May, the outcome of which could shift the delicate balance in the governing coalition.
The anti-establishment 5-Star has always opposed amnesties - a frequently used policy in Italy where people or companies can avoid being pursued for tax dodging by paying a fee.
Premier Giuseppe Conte told reporters in Brussels that he would review the draft law line by line when he returns Friday to Rome.
Giuseppe Conte also faced discontent over the 2019 fiscal plan at home, calling a meeting of the government for Saturday to stave off an emerging internal rift over conditions of a partial tax amnesty.
Rutte said in a statement that he expressed Dutch concerns regarding Italy's budget plans and said he was giving "full support" to the European Commission, which is vetting the draft after having expressed its skepticism.
Conte said on arrival at the European Union summit that the budget plans boost welfare spending, cut the retirement age and hike the deficit, and acknowledged they were unlikely to please the commission.