Commenting on about an alleged rape of an Italian woman by an African man, Dolores Valandro, a councillor in the northern city of Padua posted a picture of Italy's integration minister Cecile Kyenge, commenting below: "Why doesn't anyone ever rape her so she can understand what the victim of this heinous crime can feel?"
Northern League secretary in the northeast Veneto region, Flavio Tosi, deplored Valandro's "unspeakable" comments and said she woudl be expelled from the party.
Valandro's "violent, stupid" comments were earlier condenmned by the Northern League's whip in Italy's Senate upper house of parliament, Massimo Bitonci, who vowed disciplinary action against her.
He said he had told Valandro to remove the remarks from her Facebook profile and apologise.
Rightwing extremists have attacked Kyenge online since she was appointed integration minister in April and magistrates are probing racist insults and threats sent the minister.
Several Northern League members have made offensive comments about Kyenge, a 48-year-old doctor who was born in the Democratic Republic of Congo and moved to Italy to study medicine.
A Northern League Euro-MP, Mario Borghezio, claimed Kyenge would seek to "impose her tribal traditions from the Congo," and called the new Italian cabinet a "bonga bonga" government.
Amid an online petition to remove him, Borghezio apologised for the slurs but he was ousted from the EFD Eurosceptics group in the European Parliament.
Last month, the far-right Forza Nuova party launched an internet campaign called 'Immigration Kills', after several recent murders allegedly committed by immigrants in northern Italy.
The group attacked as "absurd" proposals by Kyenge to grant automatic citizenship to children born to legal immigrants in Italy.