D.C. Code § 5-543.05
Whenever any officer or member of the Metropolitan Police force, including, notwithstanding any other law or regulation, any employee appointed pursuant to § 1-610.72, the Fire Department of the District of Columbia, or the United States Park Police force is changed or demoted from any class to a lower class, the Mayor of the District of Columbia, or the Secretary of the Interior, as the case may be, may, in his discretion, in changing or demoting such officer or member, fix his rate of compensation at any rate provided for the class to which he is changed or demoted which does not exceed his existing rate of compensation, except that if his existing rate falls between 2 step rates provided in such lower class, he may receive the higher of such rates.
D.C. Code § 5-543.05