White Mountains Insurance Group, a Bermuda company that sells insurance and reinsurance globally, on Friday said its largest US unit has been subpoenaed by Massachusetts Attorney General Tom Reilly.

In a regulatory filing, White Mountains said OneBeacon Insurance Group, a wholly-owned subsidiary based in Boston, "received a civil investigative demand requesting documents and seeking information" on conduct between OneBeacon and insurance brokers.

White Mountains said it was "cooperating" with the demand which it believed was "part of the ongoing, industry-wide investigation" into illegal bid rigging between insurers and brokers that use them to meet their clients insurance and reinsurance needs.

White Mountains said previously that OneBeacon was subpoenaed by New York Attorney General Eliot Spitzer last December for information on unspecified transactions.

And in June, White Mountains said that OneBeacon had been subpoenaed by Connecticut Attorney General Richard Blumenthal for documents and other information about how the company did business with insurance brokers.

In an industry wide investigation, some brokers have been charged with illegal bid rigging activities with insurers to create the sham appearance of competition. Also under regulatory scrutiny are incentive payments that insurers commonly paid brokers to win a steady stream of business. Most brokers have said they no longer receive these types of payments, commonly referred to as contingent commissions.

The spotlight was turned on questionable broker/insurer business practices last October by Mr. Spitzer when he filed a civil suit against leading worldwide broker Marsh & McLennan. Marsh later settled the matter by establishing an $850 million fund to compensate aggrieved clients.

The second and third ranked brokerage companies, Aon and Willis, also later set up similar funds, for lesser amounts. In March, Aon Corporation and a related company, Aon Consulting Inc., agreed to a $190 million settlement for soliciting and accepting kickback payments to steer business to favoured insurers.

The settlement was reached with Connecticut Attorney General Richard Blumenthal, who has been, parallel to Mr. Spitzer's investigation, scrutinising practices between brokers and insurers.

Illinois Attorney General Lisa Madigan also signed on to the Aon settlement.

And in April, Willis reached an agreement with Mr. Spitzer to discontinue any illegal or questionable business practices, and settle charges by establishing a $50 million fund by July to compensate US policyholders.