Can u be terminated if you have a note from the Dr informing your employer that you should be off work for at least a week maybe even needing surgery. And your boss took you. After returning to work so they would not be short handed the manager threatened me in front of the customers.

It's employment at will UNLESS you are protected by union or contract. I don't understand if you were threatened, fired or something else.

If a Doctor said you should not return to work, you ignored his/her advice (for any reason) and returned to work - you no longer can blame a medical condition for your termination. By going back to work you ended your medical leave.

You boss took you ? Where did he take you ? Do you mean after the doctor you returned to work ? Then the boss threatened you in front of customers, Why ? What threats.

When did he fire you ?

Can you explain the time frame better.

But yes, they may fire you if you have to be gone, even if it is for a good reason.