And at the forefront of it, Bob Neill, former Conservative Party vice chairman and MP for Bromley and Chislehurst, has called for the transport secretary to resign.
Earlier this week Grayling rejected Sadiq Khan's bid to take over Southeastern in 2018, saying Transport for London (TfL) hadn't made a convincing enough business case to show the changeover would lead to better services.
"It is regrettable that I have been forced to adopt this stance and call for the secretary of state's resignation, but I will not sway from that commitment we made, nor will I allow long suffering passengers in my constituency to be used as political pawns," Neill said.
It is clear therefore that Mr Grayling's decision was not motivated by the merits of the case but by party political bias. That is not a proper consideration to take into account in deciding public policy and arguably opens his decision up to legal challenge as being irrational.
He criticised the minister's decision as "a cynical, party political move that has failed to act in the interests of London commuters", when he simply had "a dogmatic opposition to rail devolution".
In the letter written to Boris Johnson in 2013, Neill said Grayling's "real motive" was given away.
The letter seen by the Evening Standard, had Grayling writing: "I would not be in favour of changing the current arrangements – not because I have any fears over the immediate future, but because I would like to keep suburban rail services out of the clutches of any future Labour mayor."
Train drivers' union Aslef has also joined the calls. General secretary Mick Whelan said: "‘How can anyone trust anything Mr Grayling ever says again? This lie – putting narrow party advantage ahead of the interests of the travelling public – shows he is manifestly unfit for public office. If he won’t do the decent thing and resign Theresa May should sack him."
In response to the leak, Khan said "a good rail service for commuters is far, far more important than party politics" in response to the leak.
Neill said he was particularly frustrated as his constituency was filled with commuters who "are entirely dependent on the wholly discredited local franchise Southeastern" and "tired of the daily deterioration in service we have all witnessed".
Downing Street though, has rebuffed the calls for action. The Prime Minister’s spokesperson said Theresa May had full confidence in Grayling and he was doing an "excellent job" in reforming the railways.
Bob Neill's not happy with Chris Grayling...