"Everyone will be arrested and all their belongings will be taken away by sanitation," the email said.
The email was posted by LAPD critic William Gude on his @FilmThePoliceLA Twitter account.
"As always, do not approach these individuals experiencing homelessness," the email from a senior lead officer said. "I want to make sure all are there at the encampment on the 29th so I can arrest them. This is a hush hush task force."
The cleanup in Shadow Ranch Park was scheduled Thursday, but it's been postponed after the leak.
LAPD said the email was "highly inappropriate and does not in any way represent the Department's values, policies or practices related to people experiencing homelessness."
WATCH: LAPD Chief Michel Moore discusses leaked email, postponement of encampment cleanup
LAPD Chief Michel Moore discusses leaked email, postponement of encampment cleanup
The officer who wrote the email will be "provided extensive training" by LAPD's homeless coordinator's office, a statement said.
"I was horrified by the email," L.A. Mayor Karen Bass said. "We've done at least 20 Inside Safe operations, and so the spirit of that email is the exact opposite of what we believe in."
The cleanup was part of an operation called Care Plus and conducted by L.A. Sanitation & Environment.
Homeless advocate Rev. Andy Bales was also critical of the email and the possible motivation behind it.
"I know I'm reading into the email, but I think what (the officer) was saying is 'Let's not alert people that we're going to do an outreach. Let's just show up and catch them in criminal behavior,'" Bales said. "That's not what it said, but that's what I suspect."
LAPD Chief Michel Moore said police are only there to assist in any operation.
"Our presence in these encampments is not to arrest these individuals, or somehow capture people," Moore said. "Quite the contrary, we are there to provide for the safety of the sanitation workers, the outreach workers, as well as the persons who are there who are homeless."
Officials say before a cleanup operation begins a notice has to be posted.
Renheo Argandona lives in the encampment and says he's used to it.
"It happens every six months. They put up these signs and they tell us to move," Argandona said. "We move and then we come back the next day and nothing happens. It's an ongoing stretch."
Some neighbors who spoke to Eyewitness News say the area needs to be cleaned up.
"They have garbage all over the place," neighborhood resident Steven Oliva said. "Let's keep in mind while we want to be somewhat sensitive to their situation, they are at the entrance to a park where children go, so children are constantly walking past this."