The Bulls have upped the ante by accusing the Crusaders of illegal scummaging ahead of their Super 14 rugby semifinal.
The teams meet in Soweto on the outskirts of Johannesburg on Sunday morning (NZT), when Bulls captain Victor Matfield wants Australian referee Stuart Dickinson to police the scrum particularly closely.
The Bulls believe the Crusaders gain an unfair advantage in the set piece by using questionable tactics.
Their concerns, raised so close to the semifinal, might be viewed as a smokescreen, but Matfield is adamant that Dickinson has to be decisive in that area.
"They're a great scrummaging unit, but we've observed that they target the tighthead side of the scrum through illegal means," Matfield told South African rugby website keo.co.za.
Matfield acknowledged the Crusaders had one of the strongest scrums in the tournament, but felt that in the Bulls' match against the New Zealanders a fortnight ago, as well as in the Crusaders' game against the Brumbies last weekend, that they had gained the upperhand illegally.
"We'll ask the referee to watch out for that. It's a small thing but could make a big difference in a semifinal.
"I'm sure Richie (Crusaders captain) McCaw will raise some points of concern. It's not a witch hunt, we just want to make sure the playing fields are level."
Matfield, a lineout maestro and Springboks hardman, said his forwards would have to brace themselves in other areas where he felt the Crusaders excelled in their previous meeting on May 8 at Loftus Versfeld in Pretoria when the Bulls escaped with a 40-35 win thanks only to a highly contentious late try.
He praised the Crusaders' lineout and maul defence, noting that they had disrupted usually solid facets of the Bulls' game at Loftus Versfeld.
"They stole a number of our balls the last time we played and we'll have to improve there," Matfield said.
"Furthermore, they are the one team we struggled to get our rolling maul going against. It's been a big weapon for us, so we'll have to find ways of circumventing their strength in defending it."
As well, Matfield defended the Bulls' decision to rest the vast bulk of their top starting 15 in their last round robin match, a 10-38 loss to the Stormers last weekend.
He said the fruits of that decision were evident in training this week.
"I've seldom seen individuals in the squad as focused and intense as I have in our sessions this week.
"The guys are physically and mentally fresh and I feel that is a direct result of them having had a week off.
"I know there have been questions about how the break would affect our momentum, but we don't share those concerns. We've prepared well and we'll be up for the massive challenge."
