can a employer install cameras and call you at your job because your not smileing to a customer.
Of course. 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. The employee's goal should be to keep the employer happy and make the company money. That’s how they pay your wages.