Oyster cards can be used on the underground and buses
A travel watchdog has said a further delay in the introduction of Oyster cards to the London rail network would be "blatantly unfair" to passengers.
Previously, the Mayor of London Boris Johnson said most suburban rail companies would be able to use the cards by the end of this year.
However it will now be introduced next year, according to London TravelWatch.
A Mayor of London spokeswoman said they were working "to ensure Oyster is accepted" by London train operators.
The spokeswoman said: "Should any companies look like dragging their feet on this then the Mayor and Transport for London (TfL) will swiftly point out to them the tremendous improvement for their passengers this investment will deliver."
She added TfL and the Mayor's office were investing £40m on equipment at railway stations in the capital.
Sharon Grant, from London TravelWatch, said the lack of an integrated system was "ridiculous in a modern city like London".
She said: "Passengers at railway stations around the capital are walking past covered up, unused Oyster machines every day, and have been for months.
"Another delay is simply unacceptable, and it is time for the Department for Transport to start knocking heads together."
The electronic travel smartcard can currently be used on London Overground, the London underground, buses, trams and Docklands Light Railway.
TfL charges those who use the cards less than it charges those who pay for individual journeys in cash.
The change would mean that those coming in from the suburbs will be able to use one card to get around the capital.