CGU is to reduce broker commission rates on motor and liability insurance under its Bonus scheme.
In the Bonus scheme, brokers allow CGU underwriters into their offices to offer customers a more tailored approach.
A CGU spokesman said the cuts, which will take effect from June next year, will bring the brokers concerned into line with those selling CGU motor and liability products as packages.
He added that the move represented only a small part of CGU's motor and liability accounts. However, one industry source suggested that "300-400 brokers" would be affected and the account was worth "several tens of millions".
CGU would not reveal the number of brokers affected nor the reduction in commission rates.