The table-topping Bulls have "strongly" condemned a "racist incident" after a female fan was abused at Loftus Versfeld last weekend.
The Bulls' 29-20 win over the Cheetahs, combined with the Hurricanes' earlier loss to the Chiefs, saw the Pretoria-based team rise to the top of the Rebel Sport Super 14 points table.
On Sunday they will look to secure a home semifinal for their Loftus Versfeld base when they travel to Durban to play the Sharks in the final match of round-robin play.
However, the conduct of some of their fervent fan base has received a body blow following a "racist incident" before the match.
A strongly-worded statement issued by the Bulls read: "There has been a racist incident at Loftus Versfeld on Saturday prior to the Vodacom Super 14 match between the Vodacom Bulls and Vodacom Cheetahs where a woman suffered verbal abuse from a few spectators outside the stadium.
"The Blue Bulls Company (Pty) Ltd would like to strongly condemn these kinds of behaviour and we will do everything within our power to ensure that this does not happen again.
"The Blue Bulls Company (Pty) Ltd encourages any person suffering racial abuse at Loftus to press formal charges against the responsible parties.
"The Blue Bulls Company (Pty) Ltd wants to make it absolutely clear that people from all races and gender are welcome at Loftus.
"The Blue Bulls fully supported and participated in SA Rugby's 'Anti Racism' campaign and we trust that we can work together to eliminate racial conflicts in the future.
"The Blue Bulls Company (Pty) Ltd would like to request our supporters and spectators to help us to make Loftus a place were people from all races are welcome."
Fellow South African franchise the Lions were embroiled with allegations of racial abuse earlier this season.
Forwards coach Leon Boshoff had to front a misconduct hearing after claims he had verbally abused players, including using racial abuse.
He was replaced by former All Black Paul Henderson following the hearing, which ruled he had abused players but did not hold up the racially-orientated claims.
The All Blacks have locked away the Bledisloe Cup for a 13th successive season after brushing aside a feisty but limited Wallabies 29-9.