Ford's all-conquering Mustang race car has been ordered to undergo aerodynamic changes by Supercars officials.
Ongoing analysis by Supercars, including track data from the recent championship event at Phillip Island, has determined the Mustang holds an aerodynamic edge over it's Holden and Nissan rivals.
Led by DJR Team Penske's Scott McLaughlin, the Mustang has won nine out of 10 races in 2019 and eight pole positions.
Its dominance has led to rival teams claiming the new vehicle has an unfair advantage.
Supercars has ordered the Mustangs to undergo alterations to its aero package, mainly its rear wing, ahead of the night races in Perth on May 3 and 4.
Under Supercars parity regulations changes are allowed if a significant disparity exists between the competing cars.
It's the second time alterations have been forced upon the Mustang despite its initial specification being signed off in December by the championship and the three teams responsible for vehicle certification - DJR Team Penske, Triple Eight and Kelly Racing.
The Mustang and the Holden Commodores had to undergo centre of gravity changes in March after a test showed a disparity with Nissan's Altima.
Ford's global director of motorsport Mark Rushbrook expressed disappointment at the development.
"This is a world class car ... we stand by the state-of-the-art package we introduced into the series," Rushbrook said in a statement.
"From here on we will do our talking on the racetrack."