Page 27 of Pub 946 lists "Required use of ADS" (<a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/p946.pdf">https://www.irs.gov/pub/irs-pd...

I agree regarding the first point and do not identify myself with the tone used in the explanation. Regarding the second point, I must add that I am not a lawye...

According to recent cases it seems the shall in IRC code may be permissive and allows for possibility of selecting GDS vs ADS. Please review the following refer...