The 184 moderators sued Meta and two subcontractors earlier this year after they say they lost their jobs with one of the subcontractors, Sama, for organising a union. They say they were then blacklisted from applying for the same roles at a second firm, Majorel, after Facebook changed contractors.
In August, the court asked the parties to hold out-of-court settlement talks and said the case would proceed before it if those failed.
British tech rights group Foxglove said in a statement on Monday that the negotiations had broken down, accusing Meta and Sama of making "very little attempt to address core issues raised by the petitioners".
"The respondents were buying time and not being genuine. We kept waiting for them to participate ... only for them to keep asking for an extension of time and then come back every time to refuse to take accountability," the statement quoted Mercy Mutemi, a lawyer for the plaintiffs, as saying.
Sama said it was disappointed the mediation had failed, and would not comment further on the case.
"We have been successful in coming to a mutually agreed resolution with about 60 moderators outside of the mediation process, demonstrating our commitment and willingness to find an amicable, beneficial solution," it said in a statement, adding it was fully complying with all court orders.
Meta declined to comment. There was no immediate comment from Majorel.
Meta has previously responded to allegations of a poor working environment in Kenya by saying it requires partners to provide industry-leading conditions.
Sama has said it has always followed Kenyan law and provided mental health services to its employees. In August, Majorel said it does not comment on matters involving pending or active litigation.
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