may

Black’s Law Dictionary 1st Edition, page 762:

MAY,” in the construction at public statutes. is to be construed “must” in all cases where the legislature mean to impose a posi­tive and absolute duty, and not merely to give a discretionary power.
1 Pet. 46, 64; 3 Hill, 612, 615.

Black’s Law Dictionary 2nd Edition, page 767: 

MAY,” in the construction of public statutes, is to be construed “must” in all cases where the legislature mean to impose a positive “and absolute duty, and not mere­ly to give a discretionary power. Minor T. Mechanics’ Bank: 1 Pet. 46, 64, 7 L. Ed. 47 ; New York v. Furze, 3 Hill (N. Y.) 612, 615.