Some States have prescribed that the employer has to issue appointment letters to their employees. Some have not.
Going forward under the Occupational Safety, Health & Working Conditions Code, when it becomes effective, issuing appointment letters will become mandatory.
In scenario where the employee states that he/she is not been provided with an appointment letter from previous organization, the hiring organization can ask for experience letter of such employee issued by previous employer stating the employment details, and take bonafide reference checks as well.