A key Republican senator has raised concerns that the Bush administration rushed to approve the deal with a state-owned Arab company to run key American port operations.
It emerged in a Senate hearing that the Coast Guard warned late last year that it could not be sure whether the company, Dubai Ports World, might support terrorism.
Some lawmakers seized on the disclosure as vindicating their efforts to slow or stop the transaction on national security grounds.
Senator Susan Collins, a Maine Republican and chairman of a Homeland Security Committee, said a Coast Guard document suggested "significant and troubling" intelligence gaps in what was known about the Dubai company and she thought the administration was guilty of a "rush to judgment" in deciding in the company's favour.
"I believe the 45-day investigation should have been triggered by the transaction in the first place," said Ms Collins after a closed-door session with administration officials.
New York Democrat Senator Charles Schumer, an opponent of the deal, added, "If this isn't a smoking gun, it shows that there may be one undetected by the CFIUS (Committee on Foreign Investment in the United States) committee."
The CFIUS gave the go-ahead in January for Dubai Ports World to buy the assets of British-based Peninsular & Oriental Steam Navigation and take over the management of terminals at six major US ports.
On Sunday the White House agreed to the new 45-day inquiry into the matter, a face-saving compromise that gives President Bush, who has backed the takeover, more time to quell a bipartisan uproar.
But at the end of the review period, Mr Bush will have to authorise or reject the agreement.
Dubai Ports World requested the extra review after the explosion of concern on Capitol Hill about handing over management at US ports to a firm owned by the government of Dubai in the United Arab Emirates.