Given controlling precedent of summary affirmation in an earlier case by the U.S. Supreme Court, state law requiring employers to process labor union dues check-off cancellation requests within 30 days is preempted as regulation of private conduct within the scope of labor-management relations and the Taft-Hartley Act.
http://media.ca7.uscourts.gov/cgi-bin/rssExec.pl?Submit=Display&Path=Y2018/D09-13/C:17-1178:J:Manion:dis:T:fnOp:N:2217949: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.