I have not come across any rule or guideline that says that the seniority of a government servant may be adversely affected by grant of extraordinary leave without pay.
However, Rule 25(2) of the Central Civil Services (Leave) Rules, 1972, provides that wilful absence from duty after the expiry of leave renders a Government servant liable to disciplinary action. Therefore, if the extraordinary leave has been on account of wilful absence, the authority concerned may initiate departmental action, which may directly or indirectly come in the way of the promotion or may be even in the way of the continuation of the service itself if the absence from duty is abnormally long.
Dr. Ashok Dhamija is a New Delhi based Supreme Court Advocate and author of law books. Read more about him by clicking here. List of his Forum Replies. List of his other articles. List of his Quora Answers. List of his YouTube Videos.