Two whistleblowers described in a BBC Panorama survey on anti-Semitism in the Labor Party said they were now considering suing the party.
Former officials Sam Matthews and Louise Withers Green said they believed they had been defamed by the Labor Party in its response to their allegations.
The program – presented on Wednesday – included claims that personalities such as Jeremy Corbyn's communications director, Seumas Milne, and corporate secretary Jennie Formby had interfered in anti-Semitic investigations.
In its response, the Labor Party stated that the allegations emanated from "disgruntled former officials" opposed to the leaders of Mr. Corbyn, who had "personal and political thrusts to master", questioning their "credibility" in as sources.
Mark Lewis, the prominent media lawyer who acts for the couple, told The Observer: "These are very serious words. Labor representatives acted in such a way as to destroy the reputation of the whistleblowers.
"In their efforts to destroy these people, they left it up to the courts to decide who is telling the truth. It is ironic that the bosses of the workers' party have decided to go against the workers. "
Mr. Matthews and Ms. Withers Green – who broke non-disclosure agreements – were among the eight former party employees represented in the program.
Mr. Matthews told The Observer: "The Labor Party has chosen to ignore the accusations of anti-Semitism raised by myself and other whistleblowers of Panorama, and has instead engaged in a concerted campaign to harm my name "
Ms. Withers Green told the paper that she was "incredibly disappointed" that the party had not taken any action on the issues raised in the program.
"This should be an alarm bell for our collective duty to eliminate racism. But instead, the party used all its weight to discredit us, with false and defamatory statements, "she said.
Labor denied that the remarks were defamatory and said they would challenge any legal action.
"These are justified statements of opinion. Any claim will be vigorously defended, "said a spokesman.
At the same time, Labor continues to challenge Panorama's findings, Jeremy Corbyn claiming they contained "many, many inaccuracies".
In a speech at the Durham Miners' Gala on Saturday, he said, "The program has taken a predetermined position on its own website before it is released."
Meanwhile, UN Secretary-General Len McCluskey launched a virulent attack on deputy chief Tom Watson, accusing Ms. Formby of having handled the issue while she was undergoing treatment for the cancer.
"I have a simple message for Tom Watson and his friends in the media – a simple message for Tom and his friends: you should be ashamed of yourself," he said under the applause of the crowd in Durham. Hippodrome.
"Jennie, our message to you is that the Durham Miners' Gala is with you."