Hoffenheim owner Dietmar Hopp has called for the German football authorities to act after allegedly being subjected to murder threats by opposition supporters at the weekend.
Hopp, 68, the founder of European software giant SAP, has funded Hoffenheim's remarkable rise from obscurity to the Bundesliga but along the way has attracted the ire of some rival supporters.
Borussia Dortmund fans were at the centre of the latest controversy when a section of their travelling support used chants and banners to aim abuse at Hopp during Hoffenheim's 4-1 victory in Mannheim on Saturday.
The incident echoed scenes during Hoffenheim's game with Borussia Monchengladbach last month, when a section of 'Gladbach fans chanted obscenities against Hopp.
"They have now overstepped the mark - there were calls for murder," Hopp alleged. "This is no silly little boy's joke anymore."
He added to the Mannheimer Morgen newspaper: "We need to do something decisive against it, otherwise it will start to take on momentum and become normality."
Dortmund are co-operating with Hopp in his bid to track down those involved in the unrest. A 19-year-old from Dortmund has already been taken into police custody and faces a nationwide stadium ban if found guilty of involvement.
Dortmund general manager Hans-Joachim Watzke apologised for the actions of his club's fans, calling the incident "embarrassing, shameful and unworthy".
Hopp further revealed that Dortmund president Reinhard Rauball left the stadium in Mannheim 15 minutes early "because he was so embarrassed" by the behaviour of some Dortmund fans.