On Wednesday, the EFF issued a statement calling the South African Revenue Service's interview process "nepotistic and corrupt".
The party EFF said the selection process, led by former finance minister Trevor Manuel lacked transparency and openness.
The party claimed that Kieswetter was favoured a favourable candidate because he was a relative and close business associate of Manuel.
Manuel has since clapped back at the EFF in a statement, saying he "He "will not be abused by school yard bullies".
The former finance minister said the EFF must provide evidence for the claims made against him, in the statement including that Kieswetter and Manuel are related.
In a comment on social media Responding to Manuel's statement, EFF leader Julius Malema tweeted: "He can go to hell. We are not scared of him."