The bayside city was among the last in Alameda County to abolish the protection that landlords claim was being used as cover for widespread rent avoidance. 

It forbid them from evicting anyone who did not pay rent, but the landlords say it cost them tens of thousands of dollars over the last three years. 

The unemployment rate in Berkeley is 3.8 percent - on par with the national average - and the median rent is $3,800. It is known to be a wealthy enclave with a deeply academic community thanks to its eponymous college.  

To celebrate the end of the milestone, the Berkeley Property Owners Association (BPOA) arranged a party in a bar. 

But more than 100 angry renters crashed the soiree, calling it 'deeply cruel'. 

'I went around and told our members to remain quiet, and peaceful and not engage, and they didn't,' BPOA President Krista Gulbransen told Berkeleyside.

'I don't know how it went down from there, but next thing I know people are shoving each other.'

Gulbransen herself was shoved to the ground as 'multiple fights' broke out after a group of protesters decided to enter the venue an hour into the party.

One male landlord reportedly slapped a female protester in the face, while another protester knocked a landlord's glasses off.