Walkinshaw Andretti United has been docked teams’ championship points and fined for a pre-race infringement.
WAU returned to the winners' circle at the Beaurepaires Melbourne 400 opener thanks to Chaz Mostert.
However, it was later revealed that the team had breached start procedure before the 20-lapper.
As a result, WAU was docked 30 points in the teams’ championship and fined $3000.
However, WAU remains third overall behind Red Bull Ampol Racing and Shell V-Power Racing Team.
The post-race stewards’ report confirmed the penalties "after an admission to a breach of Supplementary Regulation 5.14.2 (Pit Crew Access on Grid – During the Start Procedure, each Team will be permitted a maximum of 2 Team personnel for each Car) during the start procedure for Race 6."
Mostert takes victory
The report also revealed Jake Kostecki had been hit with a time penalty over an early-race incident.
Kostecki was involved in an incident on lap 3 at Turn 3 involving Jack Le Brocq and Andre Heimgartner.
Le Brocq suffered steering damage in the incident, with Kostecki later slapped with a 15-second penalty.
Kostecki crossed the line 12th, but drops to 15th with the penalty.
Shell V-Power Racing Team was also fined $250 for a breach of brake system requirements.
The team failed to meet the minimum rear brake pressure of 20 bar (psi) during a pit stop for Anton De Pasquale.
Cars will return to the track Saturday with Race 7 at 10:25am AEST.