the new policy allows for an american traveler who has been denied boarding a commercial airliner to petition the u.s. transportation security administration once to find out whether he or not grounded ? under legal pressure , the government will not be able to provide an explanation because of national security concerns .
the changes partially lift a veil of secrecy enshrouding a policy that has been a centerpiece of the government 's counterterrorism efforts since the september 2001 terror attacks .