DORTMUND, Germany — Campaigners have set up a dummy tank outside Borussia Dortmund’s stadium before its first Bundesliga match of the season to protest the club’s sponsorship deal with an arms manufacturer.

An activist wore a mask with the face of the company’s CEO while holding a red card on Saturday.

Dortmund had announced the signing of its three-year sponsorship deal with Düsseldorf-based Rheinmetall on May 29, three days before the team lost to Real Madrid in the Champions League final.

On Wednesday, supporter association Südtribüne Dortmund said more than 90 fan groups had agreed to make their opposition to the deal clear at the start of the second half of Saturday’s game against Eintracht Frankfurt. The association encouraged fans to bring placards and banners criticizing the deal.

Rheinmetall is the world’s largest maker of artillery ammunition and expects to make record group sales of around 10 billion euros ($11.1 billion) this year.