Protesters kicked and punched three centre-left MPs in Rome on Friday after the parliament voted into law a government decree making vaccines compulsory for all schoolchildren under 17.
Police had to intervene after MPs Elisa Mariano, Ludovico Vico and Salvatore Capone were attacked by anti-vaccination protesters outside the parliament building after being asked if they had voted in favour of the decree.
The leader of Italy's centre-left ruling Democratic Party (PD), Matteo Renzi, tweeted his solidarity with the three lawmakers, calling the attack "sheer madness".
"Three PD members attacked by anti-vax protesters. Sheer madness. Hugs to Elisa, Ludovico and Salvatore. This won't stop us," read the tweet.
The law - vehemently opposed by so-called anti-vax groups who claim parents should have 'freedom of choice' on whether to vaccinate their children or not - comes after a measles outbreak in Italy.
The measles outbreak has claimed three lives since the start of the year among 3,842 cases amid falling vaccination rates in Italy.
Parents who do immunise their children against 10 infectious diseases including measles will not be able to enrol them in nursery school. They also face fines of up to 1,000 euros if they defy the law once their children reach compulsory education age.
Italy's health minister Beatrice Lorenzin championed the law after finding that immunisation rates had fallen below the key 'herd immunity' threshold of 95 percent, seen as the minimum level required to stop the spread of contagious diseases.