"Should this acute situation remain unaddressed, our companies will have to make difficult decisions about future employee locations," the letter said.

"This will be inefficient for us but, more importantly, highly disadvantageous to the future recovery and growth of New York City," the letter added.

The letter was signed by American International Group Chairman Maurice R. Greenberg and Citigroup Chairman Sanford I. Weill.

Others signing the letter include Merrill Lynch Chairman David H. Komansky, Goldman Sachs Chairman Henry M. Paulson Jr., and Verizon President Ivan G. Seidenberg.

The letter comes at a time when legislation creating a broad federal backstop for terrorism-related losses remains stalled in the Senate, largely over the issue of tort reform language limiting legal action.

In their letter, the employers said a workers' comp-only backstop is not complicated by the debate over tort reform. Under its provisions, workers' comp is the exclusive remedy for injured workers and they may not sue their employer.

The employers said that the magnitude of potential losses involving thousands, if not millions, of employees is impossible for any large employer to absorb or any insurer to insure.

Recent modeling, the letter said, puts these losses, under certain scenarios, in the tens of billions of dollars.