The Third Ministerial Conference of the World Trade Organization (WTO) was held in Seattle from November 30 to December 3, 1999. Tens of thousands of activists for many causes gathered to protest what they saw as the WTO's favoring of corporate interests over social and environmental concerns. Heavy police response included the use of riot gear, tear gas, and rubber bullets.
These shirts were given to P-I staff that covered the WTO events. The illustration was done by staff editorial cartoonist David Horsey (b. 1951). It depicts Post-Intelligencer staff wearing gas masks in the middle of clouds of tear gas; surrounded by police (and one Darth Vader), protesters (including one in a turtle costume), and other media outlets. Horsey was the editorial cartoonist for the P-I from 1979 to 2011.