On Dec. 4, Italians will head to the polls to vote on a series of changes to the country’s institutional framework, specifically the Senate, the upper house of the Italian Parliament. On paper, it is a referendum on amending the constitution. But there is far more than that at stake, for Italy and the European Union.

The Italian government of Prime Minister Mateo Renzi took office in 2014, tasked with reviving a stagnant economy and streamlining Italy’s bureaucracy. Renzi promised much-needed reforms aimed at making Italy a more governable country by substantially reducing the scope and power of the Senate in favor of empowering the lower house, the Chamber of Deputies. The Senate would be transformed into a “Senate of Regions” with 100 senators—mainly regional councilors and mayors—while large amounts of power would be taken away from Italy’s regions and centralized in Rome. ...