Gloria De Piero refused to answer questions about how her campaigning could be squared with her frontbench role as a spokeswoman for justice issues.
Critics said Mr Corbyn’s “complete lack of leadership” on Brexit would be underlined if he allowed shadow ministers to openly oppose party policy to push for a second public vote.
Ms De Piero’s actions were revealed when she joined other Labour referendum opponents in urging fellow MPs to join their cause at a meeting staged in Westminster.
An email sent by the group, seen by The Independent, is entitled “Respect the Result: No Second Referendum” and encourages MPs unable to attend to register their opposition in order to stay “in touch”.
It reads: “We are writing to you as someone who has expressed concerns at the possibility of a second referendum.
“Labour MPs who are concerned at the implications of Labour, and parliament, voting for a second referendum, are holding a meeting.”
It adds: “If you can attend this meeting, please click YES on the voting button at the top of this email. If you cannot attend, but would like to be kept in touch, please click NO, but keep me in touch.”
Several dozen Labour MPs oppose a second referendum, but supporters hope to significantly shrink that number if the vote is whipped.
Chris Leslie, The Independent Group MP who defected from Labour, said: “Those in the Labour party who believe the public should give their consent for this Brexit must ensure Labour’s leadership do everything necessary to deliver that outcome.”
And Vince Cable, the Liberal Democrat leader, said: “There has been a complete lack of leadership from Jeremy Corbyn on this issue.”
The Independent has asked the Labour leader’s office if any action will be taken against Ms De Piero, the MP for Ashfield, in Nottinghamshire, for defying party policy.
The MP declined to discuss her frontbench responsibilities, but told The Independent: “My views on the subject are well known and I talk to colleagues all the time.”
The controversy came as nine Labour MPs used an article in The Independent to urge colleagues to unite around Mr Corbyn’s commitment to another referendum.
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