At least ten Lloyd's syndicates have withdrawn from North American property lines. And up to 50 underwriters have been made redundant as a result, according to a senior market figure.
GAB Robins national account director of North American business Paul Smith said despite massive premium hikes, insurers were reluctant to take on property risks.
Smith said: "In the North American market, rates have risen by 50% in some classes. But loss ratios have been extravagant and it has been very difficult for property business."
Smith said binding authority agreements - when an underwriter gives permission to an intermediary to accept certain risks on his behalf - were now being shunned.
This is because underwriting managers are restricting the risks an insurer can write and there is a shortage of reinsurance.
He added: "Certain agents in the US who have the authority to bind business on behalf of underwriters in the past, have not used the facilities available properly.
"The agent can choose which risks to take on in the US or place under contract in London."
He said brokers are struggling to get risks agreed and contracts placed in the Lloyd's Market with loss ratios in excess of 80% "will in most cases not be looked at".
"At least 50 jobs have been affected and there are probably ten syndicates that have or are reviewing their business plans to exclude this binding authority," he said.
Last week, The St Paul Companies announced it would "substantially reduce the US business it underwrites in London".
The move follows QBE's decision in November to write only US property from its New York office and its group syndicates.
XL Brockbank's syndicates 588 and 861 also stopped offering US Fortune 500 property accounts.