They can try to call them, but the doctor is not allowed to give out any information about you.
The doctor might be able to say "yes s/he came in today"/"no s/he didn't come in". But the doctor is not allowed to give out the reason why you went in, since this would be a breach of the Doctor-Patient Confidentiality and therefore illegal.
In summary-
The doctor can say whether you have seen him/her on that day.
But the doctor cannot tell the employer why, if you did, you went to see the doctor, unless the doctor has your permission to do so.
Yes, in some circumstances. For example, if you called in sick, an employer can sometimes require a doctor's note, which would typically state what the medical reason is that you cannot work. This can be done if the employer has a policy requiring a note. Once an employer has signed a contract with a Union it cannot later implement such a policy without renegotiating the contract.
Also, your employer can require that you have a company physical, or even periodic company physicals, as a condition of employment. Again, once an employer has signed a contract with a Union it cannot later implement such a policy without renegotiating the contract.
if you are requesting reasonable accommodation for a medical condition, you will not be able to do so without telling your employer what your illness is.
An employer is legally allowed to ask an employee why he or she is calling out sick. In addition, they can ask for evidence on the same including a letter from the doctor.
is it legal to fire someone who calls out sick for a day
Yes, your employer has every right to call in and ask if you are ok. They may also want to know how much time you need off.
no
Yes
No, unless the employer is the police.
Legally? There are none for the employer. Employee status is not secret or confidential - expect no privacy.
no
Yes, they are legally allowed to.
Yes. Legally, they are allowed to say anything that is factual and accurate.
yes
legally By filing an unemployment claim and if the state finds for the employer you can appeal the state's decision.
Legally, though local laws may vary, the employer can require the employee to report to work in a uniform without providing any assistance to the employee to acquire that uniform. Ethics of this situation are debatable. Ultimately, either you want to work there or you don't.
Legally your previous employer cannot give a negative feedback to a potential new employer. All they can do is verify employment, dates of employment, and the position held by the employee.
They can't take something that belongs to you, but you should not be making personal calls while on the job. You could be fired for that.
The only questions that are truly legal are if the employee worked their and what their position was. They can also ask if they are eligible for rehire.
If the health issues interfere with the ability to adequately do the job, the employer may lay off that employee. Employers are not legally required to support an individual who is less productive than what is expected.