Catering giant Compass announced an investigation had found "serious irregularities" in connection with contracts awarded to its subsidiary Eurest Support Services by the United Nations.
Compass said staff members had been dismissed but did not say how many.
Eurest senior management has been restructured and reports to Compass finance director Andrew Martin.
The company has also reduced Eurest’s autonomy and increased central controls.
The investigation was conducted by law firm Freshfields and accountants Ernst & Young and overseen by the chairman of Compass’ audit committee, Steve Lucas.
"This has been a highly regrettable episode for Compass Group," said Mr Lucas. "However, we have now concluded a very thorough investigation and taken appropriate and decisive action."
Compass said the irregularities were related to the behaviour of a few Eurest staff members.
"The considerable work undertaken by Freshfields and Ernst & Young gives no reason to believe that these issues extend beyond these individuals to other parts of Eurest Support Services or to the wider Compass Group," according to the Compass statement.
Compass is also cooperating with wider investigations into UN procurement by the Southern District Court of New York, the US Congress and the UN.