Ford and its teams have been lobbying for changes to the Mustang's aero package for the Great Race this weekend amid fears the Chevrolet Camaro package is too strong.
However, the changes would have fallen outside an official parity review, creating an awkward situation where support from the Chevrolet teams was required.
Unsurprisingly there was strong opposition from the GM armada which has led to the proposed changes being rejected.
That decision hasn't gone down well with the Blue Oval teams, which joined forces in a statement expressing the collective disappointment in both the decision and the overall disparity.
The statement also rules out any form of boycott this weekend, following speculation that the Fords would sit out today's opening practice session as a protest.
"Following ongoing analysis, Supercars, in conjunction with its independent CFD partner, D2H Group, have acknowledged that there continues to be a disparity between the Gen3 Ford Mustang and Chevrolet Camaro," the statement read.
"Therefore, technical parity has still not been achieved. Unfortunately, the proposed aerodynamic changes to the Ford Mustang, which have been acknowledged by all parties involved to reduce the delta between the two models, will not be implemented for the Bathurst 1000 this weekend.
Source: Autosport