A Belfast-based personal lines broker is being probed by the Police Service of Northern Ireland (PSNI) fraud unit as part of a "major criminal investigation".
The PSNI would not disclose details of the investigation, but it is understood to relate to allegations of money laundering.
A PSNI statement said: "PSNI fraud unit is currently conducting a major criminal investigation which includes examining the role and activities of a Belfast-based insurance broker."
The broker's major business lines include household (31%) and private motor (18%). It was accepted into the GISC membership in 2001.
Last month, the PSNI warned small businesses that grossing up was endemic in general insurance.
Detective chief inspector Larry Cheshire said brokers who were guilty of grossing up could be committing criminal offences such as false accounting, theft or deception.
The PSNI has urged policyholders to combat grossing up by asking brokers for more information about policies including an itemised breakdown of documents detailing commission charges.