Shadow Communities Secretary Andrew Gwynne said it was "right" that Yorkshire's Labour MPs had written to the party's ruling NEC over its ruling last week which effectively forced Mr Jarvis to choose between the mayoralty and his current Barnsley Central role.
The Yorkshire Post revealed yesterday that a letter on behalf of the Yorkshire and Humber Parliamentary Labour Group described the decision, made days before the announcement of Labour's candidate to be South Yorkshire mayor, as “undemocratic” and “an insult”.
Mr Jarvis has always said he wanted to combine the two roles while sacrificing his mayoral salary, as the devolved post will initially have “no power and no resources" and he wants to maintain influence in Westminster to get a good deal for the area and push for a 'One Yorkshire' agreement which could make the Sheffield City Region job redundant in 2020.
During an event last night in London organised by Progress, a movement of centre-left Labour party members and supporters, Mr Gwynne was asked by its director Richard Angell whether the NEC should listen to Labour party members, who backed Mr Jarvis last week.
He responded: "My understanding is that after this week's meeting of the Yorkshire and Humber Labour MPs they now written to the NEC asking them to reconsider that.
"As a Lancastrian, getting involved with Yorkshire politics is a very risky business, but I will let you into a secret, Richard.
"It wasn't looking certain as to whether there would be a South Yorkshire mayoral election because the four boroughs that make up South Yorkshire couldn't agree on the devolution deal.
"If you think that Haringey mediation was a task in itself, I had two South Yorkshire MPs, I won't name them, one was fiercely pro the South Yorkshire devolution deal, one was fiercely pro One Yorkshire, asking a Lancastrian to mediate.
"Now, given that it's only 500 years since the end of the War of the Roses, and those of you who know the hostilities that exist between one side of the Pennines and the right side of the Pennines, and I live on the right side of the Pennines, it's probably beyond my pay grade to get involved in Yorkshire politics.
"But the point is, and I think it's an important point, I think that given that Dan is going to be our candidate, and he is standing on a particular platform to members who have endorsed that, I think it's right that the Yorkshire and Humber MPs have sent a clear view back to the NEC to look at it again."
A Labour source said Mr Gwynne was expressing a personal view which was not the official position of Jeremy Corbyn or the shadow cabinet. It is understood that he is unlikely to face disciplinary action.
MPs, Mr Jarvis and South Yorkshire’s four local council leaders have all written to party chiefs to oppose the decision after members voted last week to nominate the former soldier as Labour’s candidate for the mayoral election on May 3, which he is widely expected to win .
It raises the prospect of a high-stakes battle in which the NEC could strip Mr Jarvis of Labour's nomination and appoint another candidate, in which case it is understood the MP will back out of the race.