Train conductors on the south coast route through Portsmouth have called in sick more than 1,000 times in a month, according to a rail operator they are in dispute with.
An average of 83 services are being cancelled every day due to sickness of conductors, Southern said.
The company - which operates services in London, Sussex, Surrey, Kent and Hampshire - is involved in a dispute over the role of conductors and driver-only trains.
It took the unusual step of publishing figures which show its conductors called in sick 1,066 times in the last 32 working days.
According to Southern the rate of absence has almost doubled since the first conductors’ strike on April 26.
Its data shows that in the two weeks prior to the first strike there was an average of 23 conductors off sick each day.
But since the strike that number has risen to 40, and increased to 45 in the last 10 days.
A spokesman for Southern said: “We would not usually release such information, but passengers deserve to know the reasons behind the unusually high level of train cancellations they are presently experiencing.
“For those conductors who are ill the company is offering all the support we are able to and working out how they can get back to work.
“But these figures show a remarkable and unprecedented level of sickness absence which commenced at the time of the first strike. We are presently looking into what steps can be taken to investigate this deterioration in the health of conductors across the south of England.”
By a rail union is demanding to see the personal sickness, pay and perks records of senior bosses on Southern as the bitter dispute over staffing worsened.
The Rail, Maritime and Transport union accused the train operator of “coming within an inch” of releasing the personal medical records of its frontline staff as part of their justification for a series of cancellations.
The union said the sickness figures published by Southern were “pure fiction” that bear no relation to what workers were reporting on the ground.
The union claimed GTR is deliberately under-staffing services so it can cancel them at the last minute and try to blame the workforce.
RMT general secretary Mick Cash said: “In my 35 years in the trade union movement I have never before come across a train company that has such a raw and vicious hatred of its frontline workforce.
“These top bosses at French-owned GTR should release their own personal sickness, pay and perks records so that the public can judge their performance in the glare of publicity rather than these jokers taking pot shots at their safety-critical workforce anonymously from the shadows.
“Anyone who uses Southern/GTR services knows that daily cancellations were a way of life long before the current dispute.
“The company have now resorted to running services deliberately short staffed so that they can knock lumps out of the workforce when they are inevitably pulled. They are a disgrace and they have chosen to go to war with their staff and passengers instead of getting on with running a safe and reliable railway.”
The union is in dispute with Southern over the role of conductors which has led to strikes.