A club press release said Hartlett had not met "the uncompromising standards expected by the playing group", despite the drinking session being described as "quiet".
Port's football operations manager Peter Rohde said: "Hamish went out for a few drinks with friends on Sunday night, after returning to Adelaide following the game against Geelong.
“It was a quiet catch-up with mates, but a player's recovery must come first and his actions were outside of the standards the playing group itself has set."
The club has fined Hartlett $2500, with a further $2500 fine being suspended. It will be held over and enforced only in the event of any further breach.
"After working so hard to put his injury frustrations behind him, and to work his way back into our 22, Hamish knows he’s let himself, his team-mates and our supporters down," Rohde said.
"There is no doubt Hamish has learned from this experience, and we expect that he will make better decisions in the future. We look forward to a significant contribution in Saturday night's clash with the Crows."
