Why I don't shop at WalMart
Lots of US companies resort to these tactics. There's a billion dollar industry, usually law firms, focused on breaking unions and defeating union organizing. Pretty much any organization that contributes to ALEC, American Legislative Exchange Council, is going to be anti-union too. The Koch brothers are big contributors to ALEC.
I refuse to shop at Walmart. When I drive past, the lot is alway full. Ugh.