Former Prasa CEO Lucky Montana, the man who claimed he was the only state employee to resist the Guptas' advances, is expected to testify at Parliament's state capture inquiry on Tuesday.
Montana will surely be grilled by members of the committee over an alleged meeting between him, members of the controversial business family and deputy minister of public enterprises, Ben Martins.
His testimony could shed more light on the influence the Guptas have over the department of public enterprises and how they used this to gain contracts at state-owned enterprises.
Last year, at a media briefing, Martins admitted that, during his tenure as transport minister, he had arranged a meeting with Montana and Tony Gupta over concerns that the family was allegedly forcing the replacement of Montana and then Prasa board chairperson, Sfiso Buthelezi.
But Montana, who was axed in 2015, hit back. He said Martins had invited him to his home where Gupta and President Jacob Zuma's son, Duduzane, later arrived. Montana claimed the pair tried to coax him into manipulating the rail agency's project to procure new trains in their favour.
The letter told of repeated lobbying efforts by the Guptas on behalf of China South Rail (CSR) to get control of the R51-billion tender for new passenger trains.
Montana wrote: "I had taken issue with the representative of the Gupta family over what I considered to be attempts on their part to 'extort' money from [the bidders]... I must also add that the Guptas have presented a plan that I and other people have been allocated shares within CSR, the plan which I rejected contemptuously in the presence of our minister."