Aon Commercial is to charge clients up to 6% extra by withdrawing free premium finance that is offered by its panel insurers.
According to sources within the company, the broker is to replace the offer of free finance from the likes of Norwich Union and Allianz Cornhill with its in-house financing arm Cananwill.
The 6% change also represents a 1.7% hike for clients already using Cananwill.
An Aon employee said: "Staff are uncomfortable about implementing these new costs but have been advised by their directors that there will be no dispensation permitted."
He said internal calculations suggested it would bring in around £800,000 additional income.
Staff also expect panel insurers to pay Aon additional over-riders as a result of savings made on not financing the interest free facility.
In a statement, Aon said: "This is just one option from a range of payment facilities we offer clients, which also include full payment of the premium on demand, and credit card payments."