The balloons carry a pro-Article 18 message

Italy currently has the most rigid labour market in Europe and economists say the government needs to go much further if it is to succeed in making its economy competitive.

This is one reason why the unions have taken a stand on Article 18.

They see the government's plans to change it as the start of a slippery slope which could see other rights and guarantees gradually eroded.

The country's three main unions have a history of poor relations but this issue has united them.

Despite six months of negotiations, neither side has shown signs of any willingness to budge.

The government, with a comfortable majority in both houses of parliament, has threatened to implement the changes without union agreement.

Bargaining chip

However, a few days before Tuesday's general strike, Mr Berlusconi held out the prospect of talks, which two of the three big unions have agreed to attend.

The government is expected to propose, in return for agreement to its changes to Article 18, the creation of a proper unemployment benefit fund, to provide protection for workers who lose jobs with small and medium-sized companies.

A benefit system funded by employers' and employees' contributions exists to help people laid off from large Italian companies, but not the millions who work for smaller employers.

Correspondents say at least one of the big unions is likely to be interested in agreeing a deal with the government along these lines.