Late on Wednesday, senators approved Mr. Milei’s contentious economic reform proposal by a vote of 37 to 36.
Thousands of people gathered outside Congress to express their opposition to the plan, which gives the president—a right-wing economist—broad authority over energy, pensions, security, and other matters.
According to authorities, the violence resulted in at least 20 police officers being hurt and nearly a dozen demonstrators being taken into custody.
Protesters doused two cars in gasoline, which they then set ablaze, turning the central square into a battlefield covered in smoke.
Additionally, they threw sticks, stones, and Molotov cocktails at the police, who responded with tear gas, pepper spray, and water cannons.
The measure includes provisions for privatizing public companies and promoting investment in an attempt to transform an economy that is struggling with inflation that is close to 300 percent.
However, some demonstrators worry that it will expose them even more to growing rates of consumer inflation and unemployment.
“The lives of Argentineans are in conflict. The goal of having zero inflation and no economic activity is something we have repeatedly ingested as poison, according to social activist and protestor Luis D’Elia.