A violent May Day demonstration in Berlin resulted in more than 50 police officers injured and over 250 participants detained, the GdP police union in the German capital said on Sunday.
Three police officers were treated in hospital with broken bones, GdP state vice president Stephan Kelm said.
On Saturday, after mostly peaceful workers' rights rallies, clashes broke out at a leftist protest attended by 8,000 to 10,000 people in the city's Neukoelln neighbourhood.
Police responded with pepper spray as the crowd threw objects and lit small fires.
"These are clear signs that this is not about political expression, but that the basic right to freedom of assembly is being abused to legitimize serious crimes," Kelm said.