Staff in Aon's under-performing specialty division fear for their jobs after a critical internal email from UK chief executive Dennis Mahoney singled them out for failing to hit targets.
The email came in the same week as Aon announced it would be making staff cuts as part of a restructure to reflect a new transparent approach to broker compensation.
Aon's property, global risks, and power and construction arms are understood to be under particular threat because they have historically been the most dependent on contingent commissions.
A source close to Aon said: "There is a widespread belief that the email was a veiled management warning to those sections of the business most likely to face cut-backs."
He added: "Certain divisions like energy have been haemorrhaging business since Spitzer and will therefore be hit first."
Aon is understood to have drafted in management consultant McKinsey to help put together a complete post-Spitzer overhaul dubbed Operation Inflection by management.
Greg Case, the broker's president and chief executive, said: "It is clear that for Aon to continue to deliver operational excellence to our clients and to all our stakeholders, we must implement a number of changes within our UK operation.
"This means that there will be a reduction in the size of our workforce. However, it is too early to speculate around numbers."
A spokeswoman for Aon said: "The review is ongoing and we cannot confirm at this stage which areas of the business are likely to face staff reductions. Changes are likely to begin towards the end of the year."