The 24-year-old does not want to extend his contract - having rejected a new deal at the start of the summer - and has now left Posh in no doubt of his intentions.
According to reports, Tomlin had previously spoken with manager Darren Ferguson and director of football Barry Fry about his desire to move on but following recent public valuations of £12million by the club he felt he had no option but to submit a formal transfer request.
It is understood Tomlin, who is keen to play at the highest level possible, wanted the club to consider any reasonable offer for him rather than price him out of a move with unrealistic valuations.
Tomlin was Peterborough's top scorer last season with 13 goals and has scored 35 in 130 appearances since joining from Rushden & Diamonds for around £150,000.
He has been linked with Scottish champions Celtic, newly-promoted Premier League side Crystal Palace and Championship clubs Huddersfield and Brighton.