Twickenham - Australia backs Kurtley Beale and Adam Ashley-Cooper were dropped for Saturday's match against England at Twickenham after bringing women into their hotel room near Cardiff earlier on tour, coach Michael Cheika confirmed on Friday.
The incident took place following Australia's 9-6 defeat by Wales in Cardiff on November 10.
Australian media reported that three women, said to include Ashley-Cooper's sister-in-law, were out of the hotel by 22:30 local time.
But Wallabies' team rules state guests are not allowed in players' rooms.
Cheika, speaking to reporters at Twickenham on Friday, said he had only become aware of the incident earlier this week which was why no action had been taken prior to the 26-7 win over Italy in Padua last Saturday - a match where Ashley-Cooper started on the wing and Beale came off the bench.
"It is a relatively minor inter-team rule we have," said Cheika, who was flanked by Wallaby captain Michael Hooper at the press conference.
"The leadership group came to me earlier in the week and asked me to deal with it in a way I thought was appropriate and I thought this was the appropriate way."
Hooper said being involved in ruling out his experienced team-mates from the Cook Cup clash had been the toughest decision of his captaincy career.
"It's extremely hard. There's no way around it. We're all mates wanting to see each other do the best but the team comes first, and being genuine," he insisted.
The flanker added: "That's the direction we've got to go, these small steps to putting the team first are going to have a great outcome in the end."
Both Ashley-Cooper and Beale, who have exactly 200 caps between them, took part in the Wallabies' training session at Twickenham on Friday, with Cheika stressing that at no stage had their selection for the England match been "guaranteed".
"They were very apologetic. They realised their error and they have been trying to help the other players get ready for tomorrow's game," said Cheika.
"I know you'll be writing about this now, but I'll be doing everything I can to make sure you are writing about an Australian victory on Saturday."
The Wallabies were already reeling from the loss of star back-row David Pocock, ruled out of the England game with a neck injury earlier on Friday, when news of Beale and Ashley-Cooper's exclusion became public.
15 Elliot Daly, 14 Joe Cokanasiga, 13 Henry Slade, 12 Ben Te'o, 11 Jonny May, 10 Owen Farrell (co-captain), 9 Ben Youngs, 8 Mark Wilson, 7 Sam Underhill, 6 Brad Shields, 5 Courtney Lawes, 4 Maro Itoje, 3 Kyle Sinckler, 2 Jamie George, 1 Ben Moon
Substitutes: 16 Dylan Hartley (co-captain), 17 Alec Hepburn, 18 Harry Williams, 19 Charlie Ewels, 20 Nathan Hughes, 21 Richard Wigglesworth, 22 George Ford, 23 Manu Tuilagi
15 Israel Folau, 14 Dane Haylett-Petty, 13 Samu Kerevi, 12 Bernard Foley, 11 Jack Maddocks, 10 Matt Toomua, 9 Will Genia, 8 Pete Samu, 7 Michael Hooper (captain), 6 Jack Dempsey, 5 Adam Coleman, 4 Izack Roda, 3 Sekope Kepu, 2 Tolu Latu, 1 Scott Sio
Substitutes: 16 Tatafu Polota-Nau, 17 Jermaine Ainsley, 18 Allan Alaalatoa, 19 Rob Simmons, 20 Ned Hanigan, 21 Nick Phipps, 22 Sefa Naivalu, 23 Marika Koroibete