For the first 33 minutes of Friday’s match between the Portland Timbers and Seattle Sounders, groups of supporters for both teams stayed eerily silent. This MLS derby match is often a breeding ground of fervent fandom, as the Timbers Army, Gorilla FC and the Emerald City Supporters are regarded as three of the most passionate fan groups in the league and this was a big meeting for both teams. But on Friday they had a message to send.

The groups were protesting the league’s ban on political signs, in particular the use of the Iron Front logo. The groups believe that the World War II-era symbol, which was used by an anti-Nazi organization, should be allowed in the stadium because it represents an opposition to fascism.

The Nazi regime banned the symbol in 1933, hence the selection of the 33rd minute to end the silence. As the 34th minute began, both groups broke out into chants and a number of fans waved flags with the Iron Front logo on them.

In a joint statement released before the game, the three supporter groups called for MLS to rescind its ban on the Iron Front flag, to remove the word “political” from its ban because it is “inherently arbitrary” and to work with international experts on human rights to craft new language in the fan code of conduct.

The Timbers issued an open letter to their supporters earlier in the week defending the ban and saying the organization still stood “steadfast against fascism.” The club reiterated that fans can still wear T-shirts, pins or scarves with the logo on it, they just can’t wave a flag.

“Most of the broader public are unaware of the Iron Front and its historic meaning,” the letter said. “Instead it is widely associated with its frequent use by antifa, often in the context of violence at protests or counter protests. The Iron Front symbol is clearly different than a national symbol like the American flag, that some have tried to argue has been misappropriated by certain groups.”

In a statement to Yahoo Sports, MLS president Mark Abbott said the ban on political signage exists “to support the overwhelming majority of MLS fans who come to our stadium to enjoy a great soccer game.”

Before kickoff, the starting lineups of both squads posed with a banner saying “Anti-Fascist” and “Anti-Racist.”

After the match, a 2-1 win for Sounders, Timbers defender Zarek Valentin wore a shirt with Iron Front logo on it in the locker room.

Read more: