You're completely missing the point. You're obviously from somewhere civilized, where ordinary employees get actual, spelled out contracts that specify how many hours they're to work each week.
US employees don't get that sort of thing. At best, we get a not-actually-a-contract "offer letter" that says something about here is the job you're being offered, the salary, and the job description (generally including the weasely phrase "other duties as assigned." Because we don't have binding contracts with our employers, we don't even have that baseline of "a contract that outlines a 40 hour work week."
Trying to close the circle here, there are exceptions to at-will (e.g. discrimination laws) but AFAIK this bill [0] does not add "less than perfect responsiveness" to that list of improper reasons.
Instead it provides a mechanism for employees to complain to government authorities who can fine the company.
[0] https://legiscan.com/CA/text/AB2751/id/2965645