Thank you very much.
I think the best way to address your questions is by explaining what your employer can do, rather than what they cannot.
Generally speaking, employers have very vast discretion over how they choose to run their business, including how they pay their employees. The terms of employment can be changed at any time absent an express agreement to the contrary, as employment is "at will" absent such an agreement. It doesn't matter whether the new terms are fair, or how well the company is doing.
Really an employer's only limitations when it comes to pay are that they must pay minimum wage (presently $9/hr in CA) and overtime when required. A "commission only" compensation structure is permissible, provided that the employee's net pay each pay period is equal or greater than minimum wage for the number of hours they have worked. For example, in a standard 80 hour biweekly pay period, an employee at minimum wage would be entitled to at least $740. If the employee's commissions during that pay period exceed $740, then the employer has met its minimum wage obligation. If the employee's commissions are less than this amount, then the employer must make up the difference. The employer must also pay overtime for hours worked in excess of 8 per day or 40 per week.
While you are rightfully upset by the fact that your employer is not requiring you to spend time on "non-commissionable" activities, that is actually not illegal. Your employer can require you to engage in any sort of activity that they deem is necessary for their business. Again, the only requirement is that your paycheck at the end of the pay period equals or exceeds minimum wage. The fact they are decreasing your profit potential is not illegal, it is just reason to leave the job in favor of somewhere that you can make more money.
If you believe that your employer has failed to pay you at least minimum wage in a pay period (it wouldn't matter if you got more than minimum wage the next pay period--your employer can't "average" pay periods to satisfy the minimum wage requirement, it is judged separately each pay period), or if you have been denied overtime, your best recourse would be to file a wage claim with the Department of Labor Standards Enforcement. This is a free administrative claims process that does not require an attorney. Furthermore, a wage claim is a form of legally protected activity. This means your employer will be legally prohibited from retaliating against you, and any adverse employment action which you can link to the filing of your complaint with give rise to an entirely separate legal claim for damages.
Ultimately, though, your best recourse here may be to leave for a job where there is better earnings potential and you are treated m ore fairly, as while you do have certain minimal rights, those rights do not require your employer to be fair or to earn what you deserve for the work you are performing.
I hope that you find this information helpful. Please do not hesitate to let me know if you have any questions or concerns regarding the above and I will be more than happy to assist you further.
If you do not require any further assistance, please be so kind as to provide a positive rating of my service so that I may receive credit for assisting you. Very best wishes moving forward.