Four police and two demonstrators sustained minor injuries after a mass protest turned violent in front of the Romanian parliament in Bucharest on Wednesday night, police said.
Twenty protesters were also arrested and a number of Molotov cocktails were seized, according to a police statement.
Trouble started when a small group of sports fans in the middle of the otherwise peaceful protest started throwing fireworks and other objects at police. Authorities then fired tear gas, causing the demonstrators to disperse.
Estimates of the crowd in Bucharest went as high as 100,000, with thousands more in at least 46 other cities and towns.
For days, there have been peaceful demonstrations against the country's government, which came to power on January 4, after it announced plans to reduce penalties for corruption.
On Tuesday, the government, led by the Socialist Party PSD, approved a decree decriminalizing certain abuse of power offences.
According to the new decree, an official will go to jail only if they cause damage in excess of 200,000 lei (47,500 dollars). The decree, passed by cabinet, went into effect immediately.
The rule also allows for corrupt officials to escape punishment completely in some instances, if the crime occurs between members of the same family.
Romania's judicial watchdog complained to the Constitutional Court about the regulation on Wednesday, and the court will now decide on its legality.