Gabriel Zakuani, Nathaniel Mendez-Laing, Emile Sinclair and Tyrone Barnett have all been told that they can leave, though details surrounding the situation are still unclear.
In a statement released by the club, the Posh revealed that there had been a breach of discipline but added that they would make no further comment.
"Peterborough United are disappointed to report that Gabriel Zakuani, Nathaniel Mendez-Laing, Emile Sinclair and Tyrone Barnett have been transfer-listed and fined by the football club following an internal investigation into a breach of club discipline," the statement read.
|20/1||Peterborough are 20/1 with Bet365 to lose 3-0 to Blackburn in their next Championship match|
Mendez-Laing only arrived at the club during the summer from Wolves, while Barnett and Sinclair both made big-money moves from League Two sides last season.
However, captain Zakuani has made over 100 appearances for Peterborough since joining in 2008.
Peterborough - who are managed by Darren Ferguson, son of Manchester United's Sir Alex Ferguson - are currently 23rd in the Championship table, having taken just 12 points from their first 16 games of the season.