A general strike has paralysed transport and shut schools and hospitals across Italy, as workers protest against labour market reforms.
Scuffles broke out between the police and some protesters in the northern cities of Milan and Turin. Rallies took place in all major cities.
Trade unions say the government's reforms would endanger job security by making it easier to dismiss workers.
But Prime Minister Matteo Renzi says Italy needs mobility of labour.
The centre-left Democratic Party (PD) leader will have to find a way to overcome the striking unions' opposition - something his many predecessors failed to do, the BBC's James Reynolds reports from Rome.
Mr Renzi is under pressure from his European partners to revive the Italian economy - Europe's fourth largest - which is mired in recession and laden with debt.
His flagship reform is a "Jobs Act" aimed at loosening workplace restrictions and reducing Italy's 43% youth unemployment.
The unions say existing regulations are necessary to protect workers from being sacked by unscrupulous companies. They fear the spread of a "hire-and-fire" culture.
Angelo, a metal worker, told the BBC in Rome: "If there are demonstrations every day in Italy it's not because people are stupid, but because they're tired that the government always takes it out on the most vulnerable groups."
Thousands of union members took to the streets on Friday, from Milan to Palermo in the south.
The industrial action is the first-ever by two of Italy's largest union confederations against a centre-left government.
Centre-left administrations have traditionally had close relationships with the unions.
Correspondents say it is a sign of internal discord within Mr Renzi's own party, with some members of his Democratic Party joining the marches.
In recent years, a series of Italian governments have tried and failed to reform the country's employment laws.
GDP has fallen by 0.4% in the past year, and in the decade to 2010 only two countries had lower GDP growth than Italy - Haiti and Zimbabwe.
Are you taking part in industrial action? Have you been affected by the strikes? You can share your experience by emailing email@example.com.
If you are willing to be contacted by a BBC journalist, please leave a contact number.