42 USC 7472 - Initial classifications

(a) Areas designated as class I 
Upon the enactment of this part, all
(1) international parks,
(2) national wilderness areas which exceed 5,000 acres in size,
(3) national memorial parks which exceed 5,000 acres in size, and
(4) national parks which exceed six thousand acres in size,

and which are in existence on August 7, 1977, shall be class I areas and may not be redesignated. All areas which were redesignated as class I under regulations promulgated before August 7, 1977, shall be class I areas which may be redesignated as provided in this part. The extent of the areas designated as Class I under this section shall conform to any changes in the boundaries of such areas which have occurred subsequent to August 7, 1977, or which may occur subsequent to November 15, 1990.

(b) Areas designated as class II 
All areas in such State designated pursuant to section 7407 (d) of this title as attainment or unclassifiable which are not established as class I under subsection (a) of this section shall be class II areas unless redesignated under section 7474 of this title.