The action stems from Greenpeace's concerns with pulp and paper manufacturer Resolute Forest Products over its operations in the Boreal Forest. Resolute has its headquarters in Montreal.
Greenpeace's Quebec director Nicolas Mainville said the banners were meant to appear as "scales of justice."
"We want to re-establish the balance between the logging practices and the protection of our public forests," Mainville said.
In November, a group of Greenpeace activists scaled the Biosphère in Montreal, affixing a banner to it demanding the release of the Arctic 30.
The Arctic 30 was a group of Greenpeace activists arrested in Russia after some members scaled an oil drilling platform in the Pechora Sea, in the Arctic Ocean.