South Africa's national trade federation on Monday accused some financial institutions of "hypocritically and recklessly ostracizing" the business run by the South African-Indian Gupta family.
The Gupta family has been in the spotlight recently over its alleged undue influence over the South African government.
A statement from the Congress of South African Trade Unions (COSATU) said the banks had no authority to moralize on the Gupta issue.
The statement comes after several financial institutions in South Africa -- ABSA bank, First National Bank, Nedbank, SASFIN Capital and KPMG -- decided to stop doing business with the Gupta family.
COSATU spokesperson Sizwe Pamla called the decision "nothing but political posturing", saying it will not only affect the "gluttonous Guptas", but also the "innocent workers".
The COSATU, a coalition partner of the ruling ANC party, demands answers from the banks for their moves.
Some sitting and former officials, including Deputy Finance Minister, Mcebisi Jonas, have claimed that the Gupta family offered them ministerial posts.
The opposition has accused President Jacob Zuma of allegedly letting the Guptas exert their influence.
Both Zuma and the Gupta family deny the allegations.
Under mounting pressure, Zuma's son Duduzane Zuma last week resigned from a company owned by the Gupta family.
The Guptas moved to South Africa in 1993 and have since invested more than 10 billion rand (about 700 million U.S. dollars) in the country.