This chapter shall not apply to the gross sales or the gross income received by corporations which have been incorporated under any act of the congress of the United States of America and whose principal purposes are to furnish volunteer aid to members of the armed forces of the United States and also to carry on a system of national and international relief and to apply the same in mitigating the sufferings caused by pestilence, famine, fire, floods, and other national calamities and to devise and carry on measures for preventing the same.
RCW 82.04.380