I don't think I've seen him do opposition to workers rights / unions? He hasn't been constantly yelling about supporting them either, but that's different.
Closest to a negative I found in that quick search was him making fun of the Maryland Apple Store union that was asking to be allowed to request tips from Apple Store customers... while also saying that the rest of their demands sounded like good things to ask for.
E.g. a quick google for "daring fireball unions" turned up mostly articles like this one which were pro union-demands: https://daringfireball.net/linked/2021/11/24/wirecutter-unio...
Closest to a negative I found in that quick search was him making fun of the Maryland Apple Store union that was asking to be allowed to request tips from Apple Store customers... while also saying that the rest of their demands sounded like good things to ask for.