Borussia Moenchengladbach said they were "flabbergasted" by an avalanche of racist comments that poured into their website and social networks after the club's public support for "Black Lives Matter".
The club joined traditional rivals Borussia Dortmund, Schalke and Cologne in posting an anti-racism video last Friday.
"What we have experienced since then in the comments leaves us flabbergasted," said the club in an online statement, asking members "who do not share the values of Borussia Moenchengladbach, to terminate their membership".
The club has more than 150,000 members.
The joint video started by showing Gladbach's French striker Marcus Thuram, on May 31, becoming the first player in Germany to take a knee on the pitch after the death of the 46-year-old African-American George Floyd in police custody in Minneapolis. It followed with Dortmund's English attacker Jadon Sancho wearing a protest tee-shirt and also showed black players at all four clubs.
"We continue to clean up the many racist, hateful and contemptuous comments," the club said, adding that it was "deeply ashamed" of the fans who posted them.
The club thanked "the majority of the supporters who try to contradict (these hateful comments) with reasonable arguments and facts".
Following the lead of players such as Thuram, clubs, including Bayern Munich, joined in last week, with the whole team kneeling or wearing tee-shirts, jerseys or armbands bearing anti-racist slogans.
Marcus Thuram took a knee after scoring for Borussia Moenchengladbach sparking action in support from his club