Nearly a dozen years ago, I wrote a lengthy post on the meanings of "shall" and "will".  In that post, I noted that "shall" is sometimes used, particularly in Bylaws, to mean "may".   I did not consider whether "may" could mean "does".  

U.S. District Court Judge Brantley Starr plainly believes that "may" and "does" are not equivalent terms:

Specifically, the Court ordered “Southwest . . .  to inform Southwest flight attendants that, under Title VII, [Southwest] may not discriminate against Southwest flight attendants for their religious practices and beliefs.”   Instead, Southwest's notice said, “[t]he court [ ] ordered us to inform you that Southwest does not discriminate against our Employees for their religious practices and beliefs.”  Southwest's notice failed to mention Title VII, that the federal law known as Title VII contains a prohibition, and that that prohibition forbids Southwest from discriminating against flight attendants for their religious beliefs.  Instead, Southwest's notice communicated that there's nothing to see here—aside from the Court's bequeathing Southwest a badge of honor for not discriminating (which the Court did not do).

Carter v. Transport Workers Union of America, Local 556., 2023 WL 5021787, at *1 (N.D. Tex. Aug. 7, 2023) (footnotes omitted, emphasis in the original).   Highlighting the difference between "may" and "does", Judge Starr wrote: 

The Court ordered Southwest to convey a legal prohibition (Southwest may not discriminate)—not to imply the lack thereof (Southwest does not discriminate).

Id. at *5.  

As Judge Starr observed, "words mean something" and he was sufficiently unhappy with Southwest's wordsmithing to hold the airline in contempt and order three of its in-house attorneys to attend religious-liberty training consisting of at least eight hours of instructional time.  He also ordered Southwest to e-mail a corrective statement to each of its flight attendants.  

Companies adopting codes of conduct may want to take Judge Starr's ruling into account.  For example, plaintiffs' attorneys may [mis]interpret a statement that a company's employees "do not" engage in improper activities as an affirmation of fact.  However, codes of conduct are not intended to be descriptions of existing conduct.  Rather, they are intended to promote future conduct.  Therefore,  "may not" may prove to be better diction.