Published reports, citing U.S. officials, say al-Qaida has considered using tourist helicopters to attack targets in New York City.
Time magazine cites an unnamed U.S. law enforcement official as saying the information was found on computers belonging to an al-Qaida suspect who was arrested Pakistan last month.
Security is being stepped up at New York's three main heliports, and officials say the screening of passengers may begin this week.
In a separate development, U.S. Senator Charles Schumer has asked the White House to explain why the name of the al-Qaida suspect was leaked to the press last week.
Senator Schumer said the leak could hurt the war on terror.
Information for this report is provided by AP and Reuters.