What kind of obstruction do you think it is? It's absolutely obstruction in general English, there is strong objection to current federal immigration policy in general and not just to unfunded obligations it places on localities and this is a straight-up assertion of states' rights over federal supremacy. It's not legal obstruction of justice however. Employers can already do all those things on their own, completely legally, if they so willed it. It would be within their rights and even arguably an ethical obligation. What the CA law does is prohibit them from voluntarily waiving these rights when those rights impact the interests of subordinate others with their own rights and expectations of employer behavior. It's very akin to confidentiality obligations.