According to the joint investigation by BBC Panorama and BBC Africa Eye, women producing tea for major brands have been pressured to have sex with their bosses in return for work.
The BBC says more than 70 women who work on the plantations told the broadcaster they have suffered some form of sexual harassment at work.
Secret footage captured as part of the investigation shows the moment a recruitment manager for Scottish firm James Finlay & Company corners an undercover investigator and demands sex, during what was supposed to be a job interview for work on a tea farm.
Following the investigation, James Finlay and Co told the BBC it has suspended and barred the employee from its tea farms and reported him to the police.
The company also told the broadcaster that it is investigating whether its Kenyan operation has “an endemic issue with sexual violence”.
James Finlay and Co is the second largest tea company operating in Kenya’s Rift Valley, and supplies tea to Sainsbury’s and Tesco supermarkets.
Responding to the findings, Sainsbury’s told the BBC the “horrific allegations have no place in our supply chain”, while Tesco said that it is in “constant dialogue” with the company to ensure “robust measures” are taken.
Separate video reveals two managers sexually harassing an undercover investigator at a tea farm which was, at the time of filming, owned by British Dutch company Unilever.
Unilever told the BBC it is “deeply shocked and saddened” by the allegations, and employees who breached its Code of Conduct have been dismissed, and any criminality reported to the police.
The investigation for BBC Panorama, Sex for Work: The True Cost of Our Tea, airs on Monday on BBC One at 8pm and on BBC iPlayer.