About 600 Long Island Rail Road retirees will lose their disability benefits after a federal agency voted last week to halt the payments, amid a sweeping investigation into what prosecutors have called a major disability fraud scheme, according to agency documents and officials.

The agency, the United States Railroad Retirement Board, which over more than a decade granted disability benefits to hundreds of railroad retirees based on fraudulent medical evidence with little scrutiny, took the action on Thursday during a five-minute meeting at its headquarters in Chicago. The vote approved procedures under which the board will cut off the benefits, which, officials said, are costing the agency $2 million a month.

Most of the retirees will continue to receive their railroad pensions, which are separate from the federal disability benefits.

A spokesman for the Retirement Board said in an e-mail message that he was unaware of any past actions by the 78-year-old federal agency to terminate disability benefits on anything approaching a similar scale. He said disability benefits had been cut off in individual cases, but he could not say how many.