All fifty states. An employee who has a reasonable expectation that a scheduled meeting is for the purpose of discipline, has the right to request a co-worker as witness. But only a co-worker. He cannot have his spouse, brother-in-law, next door neighbor, or attorney, unless the spouse, b-i-l, neighbor or attorney also work for the same company.
If the meeting is not for the purpose of discipline, the company is not obliged to allow a witness. I believe, although I am not positive, that the company is not required to allow a witness for a termination meeting.
The company is not required to tell the employee of this right, but if the employee asks for it, and the circumstances are as described above, they must permit it.