The court froze the accounts after a request by prosecutors in connection to the July conviction of Umberto Bossi, the party's founder, and two others for fraud.
Northern League leader Matteo Salvini said the court was trying to stop the party's advance as it enjoys a “historic high” in popularity in the run-up to general elections, which are due before May 2018.
A recent poll suggested that the party, which mostly campaigns on an anti-immigrant platform, would win 15 percent of the vote if an election was held now.
“They are trying to get rid of us from newspapers, from TV, from radio and from parliament,” he was quoted by La Repubblica as saying.
“But they won't succeed. In a democracy it's the citizens who decide who wins and who loses.”
Bossi was handed a jail term of two years and three months for using thousands of euros in public money to fund an extravagant lifestyle. His son, Renzo, was also convicted in the case and given a one and a half year sentence.
Francesco Belsito, the party's ex-treasurer, received the longest sentence of three years.
Prosecutors alleged that Bossi had used more than €200,000 in funds provided by the state to political parties to pay personal expenses between 2009 and 2011.
Belsito was found to have embezzled nearly half a million euros, while Renzo Bossi more than €140,000, including several thousands to pay traffic tickets and €77,000 to buy a diploma in Albania.
Bossi, once a key ally of former prime minister Silvio Berlusconi, was forced out of his party in 2012 after the allegations emerged. Salvini has led the party since then.