At 8am today, the activists set up a large wooden barricade with two doorways across the agency's main entrance, which forces staff to choose whether they go through a "protect" or "destroy" forests entrance.
The activists counted the number of people going through each entrance, as a "poll" on staff's views on the subject. Over a two-hour period, 211 Saatchi staff entered the building, 163 through the "protect forests" entrance, and 48 through the "destroy" one.
The stunt is part of the organisation's goal to persuade Saatchi & Saatchi’s client P&G to stop buying palm oil from companies that are destroying Indonesia's rainforest. Saatchi & Saatchi works on the P&G brand Head & Shoulders.
Richard George, the Greenpeace UK forest campaigner, said: "We’ve been trying to get P&G to engage on the issue for at least eight months. If anyone understands public opinion, it’s Saatchis.
"We want them to tell their client P&G that deforestation is bad for business. They'll know that P&G's customers want to wash away dandruff without wiping out tigers. So who better to advise it to break its ties with forest destruction?"
When asked whether the team had plans to visit other agencies, he added: "P&G is not the only company we are after, and Saatchis is not the only agency that works with them."
The charity has already released a spoof version of P&G’s "thank you mum" ad. Earlier this week, it also targeted the FMCG giant’s global headquarters in Cincinnati in the US, by putting up huge posters accusing the company’s supply chain of deforestation and the death of wildlife.
The charity is tweeting about the protest and will continue to try and engage Saatchi & Saatchi on Twitter.
No one at Saatchi & Saatchi would comment on the protest.