The right to vote on policy questions in a referendum is a creature of state, not federal, law, and the referendum process is not a public forum under the First Amendment, so a state entity might legitimately dominate the process if there is a reasonable basis for it to do so.
A politician disadvantaged by the state's manipulation of the referendum process is a class of one for Equal Protection purposes, and where the conduct is valid as a general matter, the question is not justiciable. (This last bit is clearly implied, but not explicitly stated in those terms.)
http://media.ca7.uscourts.gov/cgi-bin/rssExec.pl?Submit=Display&Path=Y2018/D06-14/C:17-1227:J:Easterbrook:aut:T:fnOp:N:2170958:S:0
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.