Plans to shut dozens of ticket offices across the London Overground network have been announced.
Arriva Rail London, which runs Transport for London's (TfL) overground services, says the proposals are going through a consultation phase.
If the scheme goes ahead, the train company says 65 ticket offices will be shut.
It is a move which has angered trade unions who say the closures will displace staff.
Arriva Rail London says it is examining how tickets are sold at stations in light of the growing use of new technology - in particular contactless payments.
A spokeswoman said: "Before any ticket office closure is permitted, as is common across the rail industry, we would have to adhere to a consultation process which involves the Department for Transport, train operating companies and passenger representative."
The ticket offices will remain open while all views are considered, the Arriva Rail London added.
By Tom Edwards, BBC London transport correspondent
This "modernisation" plan sounds very similar to the "fit for future" plan introduced on the Tube.
Under that, in 2015 all ticket offices were closed and staff were moved on to the ticket line, however hundreds of posts were also closed.
Some of those have since been re-introduced after a review ordered by Sadiq Khan.
On the Overground, this review is certainly using the similar language.
How passengers buy tickets has changed dramatically and the company says all stations will be staffed, but what worries the unions is these changes will also mean job losses and lead to unsafe lone working.
Last time, the unions resisted Tube ticket office closures with a number of strikes, but they failed to stop the changes.
In light of that, if the plan is to close ticket offices on the Overground it is difficult to see how they will survive.
Two trade unions - the RMT and the TSSA - have jointly produced a "comprehensive" report which highlights the importance of ticket offices and more station staff.
TSSA leader Manual Cortes said "around 200 agency staff are being used to partially plug the gaps" caused by unfilled vacancies at stations.
"The joint union review highlights current concerns over safety, security and staffing levels."
RMT's general secretary Mick Cash said any cuts and closures would have "dire consequences for safety, services and accessibility".