Legal Question in Employment Law in California

Absolutely. They could fire you for it if they wanted, so be glad it's just an upaid day off work.

Yes.

The employer is entitled to set and change hours, duties, titles, compensation, benefits, leaves, vacations, holidays, policies, rules, etc. just not retroactively. There are no rules against 'unfair treatment' or poor management. In general, unless an employee is civil service, in a union, or has a written employment contract, they are an 'at will' employee that can be disciplined or fired any time for any reason, with or without �cause�, explanation or notice, other than for illegal discrimination, harassment or retaliation under the ADA disability, Civil Rights [age, race, sex, ethnic, religion, pregnancy, etc], Whistle-blower, or similar statutes. The employee's goal should be to keep the employer happy.