▁ag ency ' s ▁own ▁reading ▁of ▁a ▁stat ute ▁that ▁it ▁is ▁charged ▁with ▁admin ister ing . ▁ ▁Hold ing ▁The ▁Court , ▁in ▁an ▁opinion ▁by ▁Justice ▁John ▁Paul ▁Stevens , ▁u ph eld ▁the ▁E PA ' s ▁interpretation . ▁A ▁two - part ▁analysis ▁was ▁born ▁from ▁the ▁Che v ron ▁decision ▁( called ▁the ▁" Che v ron ▁two - step ▁test "), ▁where ▁a ▁review ing ▁court ▁determ ines : ▁ ▁Import ance ▁ ▁Che v ron ▁is ▁probably ▁the ▁most ▁frequently ▁c ited ▁case ▁in ▁American ▁administrative ▁law , ▁but ▁some ▁sch ol ars ▁suggest ▁that ▁the ▁decision ▁has ▁had ▁little ▁impact ▁on ▁the ▁Supreme ▁Court ' s ▁juris pr ud ence ▁and ▁merely ▁clar ified ▁the ▁Court ' s ▁existing ▁approach . ▁The ▁r uling ▁that ▁the ▁jud ici ary ▁should ▁de fer ▁to ▁a ▁federal ▁ag ency ' s ▁interpretation ▁of ▁ambigu ous ▁language ▁from ▁Cong r essional ▁legisl ation ▁relevant ▁to ▁the ▁ag ency ▁is ▁often ▁referred ▁to ▁as ▁the ▁Che v ron ▁de ference . ▁ ▁Che v ron , ▁ 1 8 ▁years ▁later , ▁was ▁able ▁to ▁invoke ▁Che v ron ▁de ference ▁to ▁win ▁another ▁case , ▁Che v ron ▁U . S . A ., ▁Inc . ▁v . ▁E ch az ab al , ▁, ▁before ▁the ▁Supreme ▁Court . ▁In ▁a ▁un anim ous ▁decision , ▁the ▁Court ▁applied ▁Che v ron ▁de ference ▁and ▁u ph eld ▁as ▁reasonable ▁an ▁Equ al ▁Emp loyment