Under Labor Code 551-552, no employee can be compelled to work more than 6 days in 7, unless the employer provides the extra days off to the employee at some other date during the same month.
Example: if you work 14 days in a row, then your employer must provide you with 2 days off before the end of the same calendar month.
That said, you are in a different situation, because you are asking for an extra 4 hours, and the employer is telling you that the only avialable hours are on the 7th day of the week. Thus, the employer is not compelling you to work -- the employer is simply telling you when the hours are available to you.
In my opinion, the employer is using the law to try to avoid telling you that you can't be full time. However, I think this may backfire, because, once the employer permits you to work that extra day, and does not give you the same number of days off by the month's end, then the employer will be subject to a violation of the Labor Code, and you can complain to the Division of Labor Standards Enforcement. At that point, if the employer cuts back your hours, you would be able to claim discrimination and that would give you a different claim against the employer.
So, if you want to play this game to its conclusion with the employer, then you can take the seven day schedule, work the remainder of the month and then file a complaint with the Division of Labor Standards Enforcement.
Hope this helps.
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