Goldman Sachs Group, Credit Suisse Group and Royal Bank of Scotland Group each borrowed $30 billion in an emergency lending program - details of which were not explained to the public, shareholders and members of Congress, Bloomberg reports.
The initiative was called single-tranche open-market operations and included 28-day loans between March and December 2008.
Lenders had to bid auctions in order to secure the money, with interest rates arranged as low as 0.01 per cent.
Chief monetary economist at Sarasota - and former head of research at the Federal Reserve Bank of Atlanta - Robert Eisenbeis said: "This was a pure subsidy. The Fed hasn't been forthcoming with disclosures overall. Why should this be any different?"
Recent analysis carried out by Professor Renee Adams of the Financial Markets Group at the London School of Economics suggested the power of the largest banks in the US is becoming so great that they could "capture" the Federal Reserve.
By Tony Aynsley