Unions said "hundreds of thousands" of Italians were participating in the strike, which includes trade unions USB, USI, SI Cobas, Unicobas, ADL and CUB Trasporti Lazio.
The USB union said the strike "called for the protection of labour rights and the welfare state" and "to say 'enough!' to Renzi's government and the social massacre".
Prime Minister Matteo Renzi's upcoming referendum and proposed constitutional reforms are a huge source of grievance, and tomorrow will see nationwide demonstrations by campaigners for a 'No' vote.
So, how might you be affected?
Rome is particularly badly affected by public transport strikes, with the A and C Metro lines completely stopped, along with the Termini-Centocelle rail route. To make matters worse, Metro line B - the only one running today - was on Friday morning affected by a technical fault in the main Termini rail station.
Bus routes and commuter rail lines in the capital also face disruption.
In Milan, local transport services are suspended between 8:15-3pm and 6pm until the end of the day, and Naples has guaranteed public transport only between 5:30am and 8:30am as well as between 5pm and 8pm.
State railway services - including links to and from Rome's Fiumicino airport - are not affected, however Intercity trains could well be disrupted or hit with cancellations.
Boat services will be hit be a full 24-hour strike lasting until 23:59 on Friday, including connection services to the smaller islands off Italy.
Flights to Italy are likely to face disruption, so if you're travelling to or from the country today, you're advised check with your airline before travelling to the airport.
EasyJet said that the airline expected Pisa, where an additional 24-hour industrial action is taking place, and Venice to be particularly badly affected. The budget airline has cancelled numerous flights and is allowing customers the opportunity to re-arrange their journeys.
Friday is also a day of general strike in tax agencies, local authorities, and many schools and universities. While a lot of schools remain open as usual, teachers' protests are taking place in cities across the country so lessons may be affected.
Hospital workers and local health authority workers are on a full-day strike too.
Rome saw demonstrations on Friday morning at Fiumicino Airport, and the Ministry of Education. These will culminate in Piazza San Giovanni, where there will be speeches, debates and theatrical performances, continuing until Saturday, when a national 'No Renzi Day' demonstration will take place in protest at his proposed reforms.
Marches also took place in the morning in Milan and Turin, while in Genoa, Cagliari and Foggia, demonstrations were held in front of the local prefecture and in Bologna an event took place in the Piazza dell'Unita.