No, they are free to speak & have policies & put up little posters. At WalMart ~15 yrs ago we were made to watch an anti-union video & it basically amounted to assurances that we can trust MGMT with anything; they will be fair & do the right thing. Lol
Now I don’t know when it came about, think it’s relatively new, but if there’s a union trying to form & the company goes out of their way to “bust” it, the union is supposed to be automatically recognized. IIRC.