May means an option. You may do something, but it is not a requirement.
49 CFR § 375.103
Terms used in this part are defined as follows. You may find other terms used in these regulations defined in 49 U.S.C. 13102. The definitions contained in this statute control. If terms are used in this part and the terms are neither defined here nor in 49 U.S.C. 13102, the terms will have the ordinary practical meaning of such terms.