An employer has a First Amendment right to force its employees to attend a mandatory three hour meeting at which it extols the virtues of President Trump -- or Gavin Newsom, take your pick -- and vociferously exhorts his virtues and strongly suggests that its employees vote for that person at the next election. The employees aren't a "captive audience" because they're free to quit their private sector jobs.
So holds the Ninth Circuit, in a panel consisting of Judges Paez, Tallman and Bennett.
Add this to the list of areas -- like unlimited campaign contributions -- in which private economic power can substantially affect (or, if you prefer, distort) the marketplace of ideas.