The notices, which came Friday night, order protesters to remove all tents, tarps and cooking equipment from Frank H. Ogawa Plaza or face arrest, the Los Angeles Times reported.
The notices, however, do not set a deadline for demonstrators to leave.
"Please, we ask you: Leave Frank Ogawa Plaza peacefully and immediately so Oakland Police can get back to work fighting the devastating crime that's occurring in our neighborhoods," the Oakland Police Officers Association said in the statement issued earlier Friday. "You have sent the world a strong message; now it is time to go home."
The eviction comes in light of violence at the encampment that started Oct. 25 when police moved in to take down the camp set up nearly a month ago.
Mayor Jean Quan allowed protesters to rebuild the camp in an attempt to calm protesters, yet many remained angry with her administration, and business leaders and the police union were upset Quan allowed the camp to continue.
Then, a man was shot at the camp Thursday.
Quan asked protesters to leave the plaza voluntarily after the incident.
"The risks here are too great," she said in a statement released on the city's Web site. "It's time for the encampment to end."
Protester Laura Long said she expects core members of the group to stay as long as possible.
"We're there for a reason," she said. "After the shooting, we were sure the city would use that as an excuse to kick us out."