The original budget for the court was set at $56.3m, but operating costs have ballooned as the enormity of the job facing the tribunal and the resources required becomes apparent.
Officials from the court are due to be questioned on the budget request by donor countries meeting at UN headquarters in New York on Thursday.
The extra funding would allow the court to add hundreds of new staff and remain in operation until 2011. Originally the court was expected to have ended operations in 2009.
The shortfall has become the most serious threat yet to the tribunal process, already battered by allegations of corruption and mismanagement amid fears of political interference.
Five former senior members of the Khmer Rouge are currently being held by the tribunal awaiting trials.
They are accused of war crimes and crimes against humanity committed during the Khmer Rouge's four years in power in the 1970s when up to two million Cambodians died.
|Up to two million Cambodians died |
under Khmer Rouge rule [AFP]
"It is hard to imagine that the court can continue to function without funds," tribunal spokeswoman Helen Jarvis told the AFP news agency earlier this month.
The UN-supported half of the tribunal has funds to last for several months more, but would also need a significant injection of cash after that.
"As the time for expiration of existing funds draws nearer, the situation obviously becomes more acute," Jarvis said.
The tribunal process has been beset with delays with the first trials not expected to begin until later this year, almost three decades after the Khmer Rouge were forced from power.
Pol Pot, the former leader of the Khmer Rouge, died in a jungle hideout in 1997 and never faced trial.
Critics say they fear the few surviving Khmer Rouge may also die before ever being brought to trial.