The right to travel is a part of the 'liberty' of which the citizen cannot be deprived without due process of law under the Fifth Amendment. If that "liberty" is to be regulated, it must be pursuant to the law-making functions of the Congress. . . . . Freedom of movement across frontiers in either direction, and inside frontiers as well, was a part of our heritage. Travel abroad, like travel within the country, . . . may be as close to the heart of the individual as the choice of what he eats, or wears, or reads. Freedom of movement is basic in our scheme of values.
Justice William O. Douglas