I think the small logo idea was so that employees could wear those shirts with a tiny logo advertising the maker. Like the small gator on one company's shirts. Googling, Locoste uses the gator while Ralph Lauren sticks a small logo of a polo player on theirs.
NOT advertising a company other than Walmart while working is perfectly acceptable, and it's easier to just ban all the logos and prints than worry about 'appropriate'. Even if it'd be 'okay' to wear something Walmart sells, it's easier to just ban everything.
That being said, the union logo thing just gets me. I know that Walmart will shut a store down rather than let it unionize, and thus I wonder how "Organization United for Respect at Walmart" won standing. Probably a very pro-union judge, I'm guessing.
BTW, If I was Walmart, I know it wouldn't be 'productive' but I'd probably have a bunch of people in inappropriate clothing that is now 'allowable' now that the dress code has been revoked show up in his court room.
Or put in a 'unless you're union' or something exception in there.
Or, as stated, go 'fine, here's your walmart polo shirt that you MUST wear while working, no modifications allowed, and you're allowed to wear khaki pants, etc... for the bottom half.
edit: 'The judge said that didn't matter because any policy that would prohibit any union insignia had to be "narrowly tailored" to avoid violating employee rights and the burden was on the employer to prove the rule was necessary. ' - I'd think it'd be the opposite of 'narrowly tailored'. IE a wide-reaching policy such as a uniform or something close to it, would show that the employer isn't targeting union insignia as opposed to all the other messes that employees of Walmart caliber will get into without direction.