Italy's energetic premier Matteo Renzi has staked his reputation on an ambitious reform agenda that he hopes will boost growth in the debt-laden country and streamline Italy's notoriously bloated institutions.
Under the system of "perfect bicameralism," the two branches of the Italian government have equal weight in confidence votes and in passing laws, something critics say slows down the political process.
The reforms aim to transform the Senate into a small chamber of regional lawmakers with sharply reduced legal powers, a move which would stop bills getting bogged down in a back-and-forth between the lower and upper chambers.
They would remove the Senate's power to hold votes of no confidence and significantly reduce the number of senators, essentially making the Chamber of
Deputies the main branch of government.
For constitutional reforms to enter into force they must be approved twice by both houses in the same term, with no more than three months between each
The bill would then be put to a referendum, meaning the whole process could take about two years.
"It's only a first step, but it's a fundamental shift", said Reforms Minister Maria Elena Boschi following the vote.
Critics on the left have accused Renzi of using the Senate bill to hide his failures to tackle weak growth in the eurozone's third largest economy, which is struggling to emerge from its deepest recession in the post-war period.