The London Assembly has passed an urgent motion calling on the transport secretary to reconsider his decision not to devolve franchise management to Transport for London (TfL).
Leader of the Labour group on the London Assembly, Len Duvall, who proposed the motion, said the issue was "far too important" to be used for party political purposes.
Duvall said the only people who will be happy about the decision will be train operators.
Services managed by TfL have some of the best performances in the country, whilst passengers on some London and south eastern suburban routes have experienced amongst the worst.
We need to move beyond political point scoring and the transport secretary needs to devolve franchise management to TfL who have proven capable of running decent services.
It's time for the Prime Minister to intervene and make this happen.
Yesterday Chris Grayling rejected Sadiq Khan's bid to take over commuter routes, saying the mayor hadn't proved his alternative would improve services.
But a leaked letter seen by the Evening Standard showed Chris Grayling had written to Boris Johnson before Sadiq Khan became mayor, saying he was against rail devolution as he wanted to "keep suburban rail services out of the clutches of any future London mayor".
Labour London Assembly member Andrew Dismore criticised the note, warning it looked like "political point scoring".
"It's the greatest shame for passengers that the minister's political point scoring has seemingly taken precedence over their needs," Dismore said.
The Assembly has also asked the chairman to write to the Prime Minister with its views on the matter.