Security problems mean the skyscraper to replace New York's World Trade Center must be redesigned, state Governor George Pataki has said.
The tower is a tribute to the victims of the 9/11 attacks
The Freedom Tower is being built on the site of the twin towers destroyed in the 11 September 2001 attacks.
Mr Pataki issued a statement following talks with New York police officials and developers of the Manhattan site.
Police fear the 1,776-foot (540-metre) building could be vulnerable to truck bomb attacks.
"A new design for the Freedom Tower is required in order to meet NYPD's security standards," Mr Pataki said after talks with Mayor Michael Bloomberg, the New York Police Department, the Port Authority, which owns the site, and developer Larry Silverstein.
The Freedom Tower's cornerstone was laid last July, but an assessment by the NYPD urged architects to rethink some elements of its structure.
WORLD TRADE CENTER SITE TIMELINE
July 2002: Lower Manhattan Development Corporation (LMDC) releases six initial design concepts and, in following months, launches global search for design and planning professionals
Dec 2002: LMDC releases nine initial designs and launches outreach campaign to engage public in planning process
Feb 2003: Memory Foundations by Studio Daniel Libeskind selected as plan
Sept 2003: Release of refined master site plan
July 2004: The cornerstone of the new building is laid
Police fear it would be difficult to protect the building against a possible truck bomb because of the heavy traffic along nearby West Street.
They have declined to talk specifically about their concerns, citing security reasons.
The building is due to be completed in 2009, but that could now be delayed by up to a year, officials have said.
"In 1993, there was a bombing at the World Trade Center, and we did not learn our lesson, and we paid for that with close to 3,000 lives," Mayor Bloomberg said on Monday.
"This is a building, particularly the Freedom Tower, that is built to be a symbol, and symbols are great if you are encouraged by the cause, and they are potentially a target by people that hate the cause."
The skyscraper is planned to be among the tallest buildings in the world after the completion.
Its projected height in feet refers to the year of the Declaration of American Independence.
The building is the centrepiece of architect Daniel Liberskind's master site plan selected in 2003.