New rules have been introduced to slow down defending Supercars champion New Zealand driver Scott McLaughlin after his rivals complained of an unfair advantage.
All Ford and Holden teams must make centre of gravity tweaks to their cars after conducting tests on 10 vehicles following complaints the new Mustang had an advantage.
Both Tickford Racing and Ford heavyweights DJR Team Penske say their dominant Mustangs will be compliant by next week's third round in Tasmania.
Mustang has claimed all six poles and races this season with DJR Team Penske's McLaughlin leading the championship.
Supercars testing revealed both the Mustang and Holden's Commodores had a COG edge over their Nissan rivals.
Details of the new rules were not disclosed but the ballast will be repositioned in Mustangs and Commodores so their COG matches that of Nissan's team.
The change is expected to impact the Mustangs more than the Holdens.
Nissans will remain unchanged.
Ballast can be placed strategically in the car to improve balance and is used to ensure the vehicles meet the minimum 1,395kg weight.
Tickford Racing - who boast the third-placed driver Chaz Mostert - said they would work with DJR Team Penske to make the necessary changes but weren't happy about it.
"While we are not thrilled with the situation that has arisen this week, we accept Supercars' decision and are working with Supercars and DJR Team Penske to make the necessary technical modifications to our cars," a statement said.
"The rules are the rules. We have won races and a championship abiding by Supercars' direction and our goals remain unchanged as we pursue more wins and championships no matter how the rulebook reads."
DJR Team Penske said they accepted the ruling but would propose a revised process for Supercars to determine COG in the future.