Sam Matthews and Louise Withers Green, who featured in a BBC Panorama investigation into antisemitism in the party, believe they were defamed by Labour in its response to their allegations.
The programme included claims that senior figures including Jeremy Corbyn’s communications chief Seumas Milne and general secretary Jennie Formby – had interfered in antisemitism investigations.
In its response, Labour said the claims came from “disaffected former officials” opposed to Mr Corbyn’s leadership who had “personal and political axes to grind” casting doubt on their “credibility” as sources.
Media lawyer Mark Lewis, who is acting for the pair, told The Observer: “These are very serious libels. Those representing the Labour party have acted in a way that set out to destroy the reputations of the whistleblowers.
“In their effort to destroy these people, they have left it for the courts to decide who is telling the truth. It is ironic that the bosses at the workers’ party have decided to go against the workers.”
Mr Matthews and Ms Withers Green, who broke non-disclosure agreements to speak out, were among eight former party employees featured in the programme.
Mr Matthews told The Observer: “The Labour party is choosing to ignore the central charges of antisemitism raised by myself and other whistleblowers on Panorama, and instead, they have engaged in a concerted campaign to damage my
Ms Withers Green told the paper she was “incredibly disappointed” that the party had not taken action on the issues raised in the programme.
“This should be a stark wake-up call about our collective duty to root out racism. But instead the party has used its full weight to discredit us, with untrue, libellous statements,” she said
Labour denied the comments were defamatory and said it would contest any legal action.
Meanwhile, in a further sign of tensions within the party, Unite general secretary Len McCluskey launched an attack on deputy leader Tom Watson for criticising Ms Formby for her handling of the issue while she was undergoing treatment for cancer.
“I have a simple message for Tom Watson and his pals in the media – a simple message to Tom and his pals: You should f****** well be ashamed of yourselves,” he told the crowd at the Durham Miners’ Gala.