If your employer overreaches and tries to tell you that you can’t weigh more than a certain amount or that you can’t drink alcohol when you’re not on the job or that you have to stop smoking you at least have a reasonable possibility of finding another job.
If the government that is supplying 50% of your total income tells you any of those things you cannot switch to a different government.
Your employer cannot require you to donate time to a charity but a UBI bureaucracy might.
An employer might influence a few thousand people with such rules. A government doing the same thing would affect tens of millions.