The commuter trains that service London are beyond the mayor's reach
Critics of London Mayor Boris Johnson say his election campaign pledge to expand the Freedom Pass for elderly transport users is not as promised.
Mr Johnson's Liberal Democrat opposition say the passes, also available to disabled people, are still restricted on Network Rail's trains.
Assembly member Caroline Pidgeon said the scheme was also likely to cost local boroughs millions of pounds.
A mayor's office spokesman said Mr Johnson had fulfilled his commitments.
People over the age of 60 and eligible disabled people were told during the election campaign that their passes for free travel, previously restricted to off-peak times, would be extended to 24 hours a day across London's transport network.
But Ms Pidgeon called the promise a "duff Christmas present" after Mr Johnson could not include Network Rail in the new Freedom Pass scheme which will allow holders to use the system before 0930 as of 2 January.
Network Rail trains include Chiltern Railways and First Capital Connect trains that serve busy commuter routes into London.
But a spokesman for Mr Johnson said the mayor had delivered every aspect of the promise that falls within his control.
"Ms Pidgeon appears to miss the point that the train operating companies are private entities and, although we are urging them to roll out this extension to their services, we are not prepared to achieve this at any cost."
Ms Pidgeon said Mr Johnson also confirmed that the cost of extending the passes would have to be born by local boroughs through council tax rates.
The spokesman said that working with Transport for London and the various borough councils to fund the scheme was "completely logical".