InterAction, which represents more than 160 American NGOs, says a bureaucratic log jam is preventing them from sending people and equipment to the region.
The delays could threaten the lives of Iraqis if war breaks out, the organisation says.
"It isn't clear the Bush administration is putting into action the concern for the Iraqi people expressed by President Bush," InterAction's head Mary McClymont said in a statement.
"The stakes could not be higher."
The BBC's John Leyne in Washington says InterAction members are questioning whether the Bush administration is really committed to helping the Iraqi people.
By law, these organisations need permission from the US Government to send money, equipment and staff to countries which appear on the State Department's list of "state sponsors of terrorism", which includes Iraq, Iran and Syria.
Chlorine license
Even imports of chlorine bleach into Iraq have to be approved.
But the completion of paperwork is reportedly taking from four to five months.
Ms McClymont said requests that the White House speed up the licensing process met with "unsatisfactory results".
The State Department expressed general support for the aid organisations and their wish to help the Iraqi people.
"But that doesn't mean that we can approve every licence for everybody to go wherever they might be thinking," a spokesman told reporters on Thursday.