The government measures are expected to bring the national deficit down from 5.3 per cent of gross domestic product to 2.7 per cent in 2012.
The strike, which was limited to four hours for public transport workers and eight for those in the public and private sectors, will be a key test of stregth for Silvio Berlusconi, the prime minister.
His poll ratings have reached new lows as unemployment has risen and the eurozone's third largest economy has struggled to emerge from its worst recession since the Second World War.
The strike has split Italy's trade union movement, which is roughly divided along political lines. The other two main unions have asked their members to stay on the job.
The strike is the latest in a series of rallies against austerity measures in Europe, with hundreds of Romanians also taking to the streets on Friday.
Dozens of protesters tried unsuccessfully to storm the presidential palace to protest the measures and demand an audience with Traian Basescu, the president.
A day earlier, thousands of people held strikes and protests across France over plans to raise the retirement age and reform the state pension.
Greece has also seen a string of protests against severe budget cuts in the face of its economic crisis.
Members of the 16-nation eurozone have rushed to approve austerity measures in a bid to restore confidence in the single currency and halt contagion from Greece's debt crisis.
After months of telling Italians they were immune to a Greek-style debt crisis, Berlusconi's cabinet in May approved an austerity plan including cuts to funds for municipalities and freezing of public sector salaries.