A woman who was ridiculed online by Italy’s far-right deputy prime minister, Matteo Salvini, is pressing charges after his post provoked a deluge of hateful messages and threats against her.

Giulia Viola Pacilli, 22, was photographed during an anti-racism march in Milan on 2 March holding a sign that read “Better to be a do-gooder and a whore than a fascist and Salvinist”. The march was attended by an estimated 250,000 people in what has been the most prominent sign yet of a pushback against the policies of Italy’s populist government.

Two days later the photo was shared by Salvini, who leads the far-right League, on his Facebook page alongside the sarcastic message “What a nice woman” followed by a laughing emoji.

The student became a target of hatred online, receiving hundreds of messages including one that asked if she would like a “gang of horny illegal immigrants” to be arranged for her.

Her lawyer, Giovanni Pintimalli, said: “Giulia’s been very hurt by all the messages, they are disgusting, and is scared to leave her home after some people said they would find out where she lives.”

Pintimalli will present a case for defamation against almost 300 people suspected of writing the comments to Italy’s postal police, the unit tasked with tackling online hatred, on Monday. The postal police said they would launch an investigation once the complaint had been received.

“It’s difficult to target the minister for a crime as the message he wrote was harmless and not defamatory,” said Pintimalli. “So the case will be against those who made the insults. But we also need to stress the fact that even though Salvini’s comment was neutral, it unleashed hate speech and he did nothing to prevent it. He’s in a powerful position and this is just an ordinary girl; he should know better than to be doing this sort of thing.”

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Salvini shrugged off the controversy, saying he would like to see the same level of indignation “towards those who write insults and make death threats against me”. On Monday his spokesman said the minister had nothing more to add.

Michele Anzaldi, a politician with the opposition Democratic party, urged the postal police’s chief, Nunzia Ciardi, to look into the case. “The gravity of the case should not be underestimated,” he wrote in a letter. “The woman’s fault was to demonstrate against the policies of the government, and have her photo posted on the interior minister’s social media profile alongside an ironic sign of dissent. This exposed the woman and her family to insults and threats of all kinds.”

Salvini continuously attacks his critics on social media, whether they be political opponents or ordinary people. He also derided women who held signs with messages opposing him and his policies during a an International Women’s Day march against gender-based violence.