The Jewish Labour Movement (JLM) will this week write to the Equality and Human Rights Commission (EHRC) asking them to investigate Labour's decision to let Chris Williamson back into the party.
ITV News understands the JLM will ask the EHRC to use statutory powers to compel members of Labour's National Executive Committee to hand over their electronic devices to discover whether or not there was a "stitch up" in the disciplinary proceedings.
The EHRC is currently investigating the Labour Party for its handling of allegations of anti-Semitism.
The MP for Derby North had his four-month suspension lifted on Wednesday by a three-person panel comprised of NEC members, against the recommendation of Labour Party staff who had investigated Mr Williamson.
He was suspended in February following his comments that the party had been “too apologetic” in response to criticism over its handling of anti-Semitism allegations.
Video footage showed him telling a meeting of the grassroots Momentum group that Labour’s reaction to anti-Semitism allegations had led to the party being “demonised”.
ITV News has learned the panel deciding Mr Williamson's fate was due to meet on Tuesday, comprised of George Howarth MP, Jon Lansman and Claudia Webbe. The meeting was however cancelled after Ms Webbe said she could no longer attend.
The panel was rescheduled for Wednesday with a different panel of Mr Howarth, Keith Vaz MP and Huda Elmi.
The Jewish Labour Movement believe the original panel would have upheld Mr Williamson's suspension and suspect 'foul play'.
They now want the EHRC to look at the conversations Ms Webbe and other NEC panel members had regarding the cancelled meeting.
A senior source in Labour leader Jeremy Corbyn's office told ITV News the original hearing was cancelled because of an "administrative mistake" and strongly dismissed any suggestion the panel was changed to favour Mr Williamson.
They added the decision came as a "surprise" to the leader's office.
MPs have been given until July 8 to say if they wish to seek re-selection in their seats.
Labour MP Stella Creasy said: “The decision to let Chris Williamson back into party in time for him to stand again as a Labour candidate is the best example yet of why we need an independent process for anti-Semitism and sexual harassment complaints and not mates’ rates."
A Labour source said: "An NEC panel, advised by an independent barrister, found Chris Williamson had breached the Party’s rules and gave him a formal sanction.
"He could face further, more severe, action if he repeats any similar comments or behaviour."
The Derby North MP, who has apologised for comments he made at the meeting in Sheffield, said on Twitter: "I'd like to express my heartfelt thanks for the avalanche of goodwill messages from grassroots members.
"I can now focus on representing local people in Derby Nth and working for a Corbyn-led Labour govt to positively transform the lives of millions. Together anything is possible!"