Under pressure from the New York City pension fund, Aon Corporation has agreed to form a senior management committee that will examine the giant insurance company’s business ties to Iran, chief executive Patrick Ryan said in a letter to City Comptroller William C. Thompson Jr. that was obtained by The New York Sun.

The announcement comes on the heels of an announcement last week by Halliburton that it won’t seek new business in Iran, also as the result of pressure from the New York City pension fund.

Mr. Thompson, in a prepared statement, said, “Aon’s decision is a significant victory for the city’s pension funds.”

As the trustee and investment adviser to $74 billion in city pension funds, Mr. Thompson has been waging a high-profile campaign since November 2002 to make companies within its equity investment portfolio review their operations for any business connections to Iran.

Currently, a loophole in the law allows American companies with foreign subsidiaries to do business in terrorism sponsoring states, as long as American management is not involved in these operations. Mr. Thompson has said in the past that one of the primary goals of his campaign is to force these companies to comply with “the spirit of the law.” Late last year, Senator Lautenberg, a Democrat of New Jersey, proposed legislation to close this loophole.

An Aon spokesman, David Van de Walle, declined to release the amount of Aon’s revenue from its Iranian operations.

He said that all its Iranian dealings were in compliance with American law. In the September 11, 2001, terrorist attacks, the company lost 175 workers in the collapse of the World Trade Center’s South Tower. City pension funds own 997,575 Aon shares, worth $22.82 million.

Aon, headquartered in Chicago, does business in Iran via two subsidiaries – Mahamy Plc and United Iranian Insurance Services Plc. Tehran, according to the Conflict Securities Advisory Group, a Washington, D.C., company that advises shareholders on how American companies are complying with laws forbidding investment in terrorism-sponsoring states.

Aon is the last of the five companies identified by Mr. Thompson – General Electric, CooperCameron, Halliburton, and ConocoPhillips are the others – to agree to conduct a formal inquiry into its Iranian operations. The other four companies agreed to either shut down business ties or to stop seeking new contracts.

The inquiry, according to Mr. Ryan’s letter, will highlight “potential financial and reputational risks” to the company. This report will be completed and released to the controller by December 31. In return, Mr. Thompson has agreed to pull the potentially embarrassing shareholder proposal.