A committee of the US Congress has voted overwhelmingly to block a company from Dubai running six American ports.
The House Appropriations Committee voted by 62 votes to two for the amendment.
Dubai Ports World is taking control of P&O, which currently runs six US ports from New York to New Orleans.
Opponents to the deal say management of major ports by an Arab-based company could jeopardise national security.
However, US President George W Bush has said such fears are unwarranted because the United Arab Emirates is a strong ally. He has threatened to veto any legislation blocking the deal.
