By Gavin Jones
ROME (Reuters) - Tens of thousands of workers marched through the centre of Rome on Saturday against Prime Minister Matteo Renzi's reform of the labour market, headed by a popular union chief who is seen by many as a possible future leader of Italy's left.
The march was organised by Italy's main engineering union, the FIOM, whose leader Maurizio Landini is trying to unite the fragmented political left into what he calls a "social coalition" against Renzi.
He accuses the 40-year-old prime minister of moving his Democratic Party (PD) too far towards the political centre, abandoning it traditional roots.
"A new springtime begins today for Italy," Landini said, surrounded by supporters waving the FIOM's red flags. "We're ready to do battle knowing we have more support than the government does."
Under Renzi the PD has become by far Italy's largest party, helped by divisions on the centre-right which has been weakened by the legal problems of its leader Silvio Berlusconi.
Saturday's march was attended by Nichi Vendola, the leader of the small, left-wing SEL party, and several prominent leftist lawmakers from Renzi's own PD.
Renzi's so-called Jobs Act, key parts of which became law last month, makes it possible for firms to fire workers for business reasons with no risk of having to re-instate them if the dismissal is ruled illegal by a judge.
A company which wrongfully dismisses workers must pay them compensation but not give them their job back as before.
Renzi says the Jobs Act will help reduce record unemployment, which stands at around 42 percent among those below the age of 25.
The government is also offering temporary fiscal incentives for firms to hire workers on a permanent basis in an attempt to reduce the widespread use of temporary contracts which offer low pay and few rights.
Data presented by the labour ministry this week showed that new permanent contracts had risen by 79,000, or 35 percent in the first two months of the year compared with the same period of 2014, as firms take advantage of the incentives.
Renzi, who says he wants to "revolutionise" Italy with institutional and economic reforms, has so far shown scant regard to numerous strikes and protests against his year-old government by workers, students and opposition parties.
On Friday he dismissed Landini's march, telling reporters: "Tomorrow there's another march against the government - no news."