PORTLAND, Ore. -- Groups of supporters of the Portland Timbers and Seattle Sounders staged a silent protest for the first 33 minutes of Friday's match involving the two teams.

The groups were protesting Major League Soccer's ban on political signage, and in particular the Iron Front symbol, which was used by an anti-Nazi paramilitary organization before World War II.

The supporters groups contend that the Iron Front symbol is intended to promote inclusion, anti-fascism and anti-racism. MLS has stated the symbol is connected to the antifa movement in the U.S. and thus constitutes a link to a political organization.

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As part of the protest, the Timbers Army group did not display any pregame tifo as it normally does and, along with Seattle groups the Emerald City Supporters and Gorilla FC, refused to engage in organized chants, songs, choreography, flag-waving and the playing of drums or trumpets, remaining silent until the end of the 33rd minute. That time was chosen to commemorate 1933, the year the Iron Front was disbanded in Nazi Germany.

As the protest ended, the Timbers Army sang "Bella Ciao," an Italian anti-fascist anthem from World War II.

In a statement released before the game, the three groups called for MLS to rescind its ban on flying the Iron Front flag, as well as to remove the word "political" from its fan code of conduct, calling the use of the word "inherently arbitrary." The groups also asked MLS to work with international experts on human rights to craft language in the fan code of conduct that "reflects and supports radical inclusion and anti-discrimination."

In recognition of the fans' complaints, both teams posed ahead of kickoff for a group photo with small banners that read "anti-fascist" and "anti-racist." The teams' Twitter accounts also posted messages reading, "Bigger than a rivalry. We stand together against fascism and racism."

Bigger than a rivalry. We stand together against fascism and racism. pic.twitter.com/pzZnRIANY9

— Seattle Sounders FC (@SoundersFC) August 24, 2019

The supporters groups' protest was largely observed by the rest of the crowd, with faint chants of "Let's go Timbers" occasionally heard. But when the clock struck 33 minutes, both sets of supporters began cheering and chanting at full volume, with numerous Iron Front flags visible in the Timbers Army section.