Mussolini, who filed an appeal before an administrative court in Rome, said she would fast until the appeals ruling is issued. News reports said the decision would be made by Friday.
The hunger strike is meant "to gather public attention and attention of the media to something that we would describe as a 'coup d'etat,' a real illegal seizing of the power," Mussolini told Associated Press Television News.
The ruling, she added, "is important for democracy."
The flamboyant Mussolini said she will stand vigil, in a van outside the court building where she submitted her appeal, waiting there until the verdict. "I will be here night and day," she told Italian TV.
On Saturday, a court ruled that a list submitted by Mussolini's small party, Social Alternative, for elections in the Lazio region included almost 900 phony or irregular signatures from voters. They included fake signatures of actors, judges and an army general.
If the court's decision is upheld, Mussolini, who wants to run for governor in the region, will not be able to stand in the April 3-4 election. She is currently a deputy at the European Parliament.
Mussolini founded Social Alternative in late 2003 after quitting the National Alliance, a right-wing party that is part of Premier Silvio Berlusconi's governing coalition. She is protesting the denunciation of Italy's Fascist past by party leader Gianfranco Fini, the current foreign minister, and said she wanted to defend Benito Mussolini's heritage.
Parties have to present a minimum of 3,500 signatures from registered voters to take part in the elections in Lazio. Mussolini contends that she has been set up by mainstream conservative forces afraid that she might take votes away from them.
The vote to elect governors in 14 of Italy's 20 regions is seen as a key test ahead of political elections next year. The vote in Lazio, the region that includes Rome, was among the most closely watched.
According to Corriere della Sera Sunday, Mussolini might have won between 4 and 9 percent of the vote - taking votes from right-wing incumbent Francesco Storace, of the National Alliance party. Storace is up against the center-left's Antonio Marrazzo, a TV journalist.