The Serious Fraud Office has requested an extra £21.1m in funding from parliament, with £15.5m sought urgently.
The demand was revealed in a statement to parliament from Solicitor General Robert Buckland, and comes six months after the SFO requested a further £10m from MPs.
The SFO operates on an annual budget of around £33m, but is able to request extra funds from parliament.
Buckland said the cost would cover “significant investigations and the settlement of material liabilities”.
However, Labour has questioned the increase, questioning whether the funding method allows Chancellor George Osborne undue influence in prosecutions pursued by the fraud watchdog.
Shadow attorney-general Catherine McKinnell told the FT: “This is the third year running that the SFO has had to go cap in hand to the Treasury for contingency funding equivalent to over half its budget.
“This sticking-plaster approach is neither sustainable nor transparent and it simply cannot be right that George Osborne [the chancellor] gets to decide which major cases should be investigated.”