Perez was on a warm-up lap for his first Q1 run when a hotlapping Hulkenberg encountered him in the middle of the racing in on Turn 13, Albert Park's slow penultimate left-hander.
The Mexican was only told very late by his race engineer that the Haas driver was behind him, with the focus instead being on preparing his flying lap.
Perez was summoned by the stewards after qualifying, in which he took third place behind Red Bull team-mate Max Verstappen and Ferrari's Carlos Sainz.
The stewards handed him a three-place grid drop, instead demoting him to sixth on Sunday's starting grid.
"Hulkenberg was on a fast lap when he approached turn 13," their verdict said.
"Perez, who was on an out lap was at the apex of the turn and Hulkenberg had to leave the racing line to drive around him. Hulkenberg was forced to lift the throttle early and brake early for that corner.
"In reviewing the audio from Perez’ car, the Stewards observed that the team was focused on the car in front of Perez that had just slowed, and did not give Perez a warning that Hulkenberg was behind him until one second before Hulkenberg arrived, and significantly too late to avoid impeding Hulkenberg.
"While the Stewards appreciate the dynamic situation facing the team and driver during the Q1 session, which was described in the hearing, the Stewards find that Perez “Unnecessarily Impeded” Hulkenberg and issue a three grid place drop, consistent with previous cases."
Hulkenberg felt the incident "cost a few tenths" as he failed to make it out of Q1.
"Maybe, because that lap I think was my first 1m17.9s also, and it cost a few tenths," he said after qualifying 16th, two spots behind team-mate Kevin Magnussen who did make it through to Q2.
"He was having Mexican siesta, I think. He wasn't looking in the mirror.
"The closing speed coming around Turn 12, it's so quick now and if you're not paying attention enough, it happens very easily and quick. But, of course, it shouldn't happen."
Additional reporting by Adam Cooper
