An Italian teacher has been suspended over a video made by her students that compared a security law drafted by Italy’s far-right interior minister, Matteo Salvini, to Mussolini’s racial laws, provoking a storm of protest against her suspension across the country.

Rosa Maria Dell’Aria was last week suspended for 15 days on half pay after an investigation by the education ministry’s provincial authority in Palermo found she had not “supervised” her students’ work.

“I am embittered,” she told the Guardian. “I am not talking about the economic damage, for the days of suspension, but about the moral and professional damage after a whole life dedicated to the school and the kids.”

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Students at Vittorio Emanuele III high school in the Sicilian capital had presented the video in January as part of a project for International Holocaust Remembrance Day comparing current events to antisemitic persecution.

The students, aged 15 to 16, compared the fascist-era racial laws introduced in Italy by Benito Mussolini to Salvini’s security decree, approved by parliament the previous month. The law left hundreds of asylum seekers in legal limbo by removing humanitarian protection for those not eligible for refugee status.

Dell’Aria, 63, defended the exercise. “That project had absolutely no political purpose nor was it intended to indoctrinate students, who have always worked freely,” she said. Teachers throughout Italy have expressed solidarity with Dell’Aria and announced a strike to protest against her suspension.

Members of the opposition Democratic party have also spoken in support of her. “Some students link Salvini to fascism, something that Salvini himself often does … and the ministry has decided on a very harsh sanction,” said Anna Ascani, the party’s vice-president.

“Is the next step a return to the [fascist youth organisation] Opera Nazionale Balilla? Do some people want to turn Italian schools into barracks?”

The Democratic party leader, Nicola Zingaretti, said: “It violates the constitutional principles of freedom of teaching and expression. In Italy extreme-right groups can do and say whatever they want while a student is prevented from expressing his disapproval.”

Marco Anello, the head of the education ministry’s provincial authority in Palermo, defended Dell’Aria’s suspension. “We have simply enforced the law,” he said. “Comparing the security decree to a racial law means offending not only Salvini but also the Italian state.”

Responding to claims he was a Salvini supporter, Anello said: “For almost 20 years I have served both right and left governments indifferently.”

Dell’Aria’s students have written to the regional education authority expressing their support. “She was always impartial and it was us who came up with the comparison,” the letter wrote. “The images in the PowerPoint presentation were not chosen by the teacher, who only gave us a hand in fixing the text from a linguistic standpoint.”

As thousands of students marched to support her in Palermo, the deputy prime minister, Luigi Di Maio, leader of the Five Star Movement party, which governs in coalition with Salvini’s League party, phoned the teacher to express his solidarity. “She needs to return at work as soon as possible,” he said.

The mayor of Palermo, Leoluca Orlando, who is fighting for migrants to freely enter EU states, has displayed the students’ video in the header section of Palermo’s municipality home page, while a group of senators for life, including Liliana Segre, expelled from her school under the racial laws, invited Dell’Aria to the Senate.

The Italian racial laws of 1938 led to the expulsion of 6,500 Jewish schoolchildren and about 700 professors, many of whom were deported to concentration camps.

Salvini said: “I don’t know who it was who proposed, controlled, ordered, or suggested [it], but for someone to put Interior Minister Matteo Salvini – who may be likeable or unlikeable – on a par with Mussolini, or even Hitler, seems absolutely demented to me.”