The protest came one day after an activist group ran a full-page advertisement in the Chicago Tribune calling the companies the "ABCs of rainforest destruction" for their role in expanding soy and palm oil plantations by clear-cutting rainforests.

A Bunge Ltd spokesman said he was aware of the accusations, but stressed the company's environmental and social record. An Archer-Daniels-Midland Co spokesman declined comment.

Cargill spokesman Bill Brady said: "We take our environmental footprint in the rainforest geographies very seriously. Cargill is committed to responsible economic development around the world."

Streets around the landmark building were gridlocked as morning rush hour traffic was diverted, while curious pedestrians gawked at the banner, which eventually became tangled in the wind before authorities removed it.

"The expansion of these commodity crops into the world's rainforests are causing mass destruction of rainforests, intensifying climate change and forcing communities off their land," said Leila Salazar-Lopez, director for the Rainforest Action Network's Stop Rainforest Agribusiness Campaign.

Soybean planting in South America has been growing rapidly as more of the oilseed, which is traded at the CBOT, is used in the production of biofuels. In the United States, ethanol is largely made from corn grown across a wide swath of the Midwest.

Wednesday's action raised concerns about CBOT building security, which has been heightened since the Sept. 11, 2001, attacks on the World Trade Center and the Pentagon.

CBOT is a subsidiary of CME Group Inc.