The protesters, about two dozen people affiliated with activist organization Stand Up Chicago and the Service Employees International Union, chanted while they circled the entrance of the tower.
The Koch brothers reportedly have expressed interest in bidding for the newspapers.
Organizers claim the Koch brothers have a "right-wing agenda" that would negatively affect Chicago and its working-class community, including fights against raising the minimum wage, unemployment benefits and consumer protections.
"I think it's time that we stand up. We have to protect our rights for good and unbiased journalism," rally leader Shani Smith said.
Tribune Co. said in February that it hired two investment banks to explore options for the company's newspapers, which also include the Los Angeles Times and the Baltimore Sun. It said no decisions have been made about whether to sell any properties.
A Tribune spokesman declined to comment on the protests.
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