or promotion. Ultimately, it was realised that if liberty is given to fix seniority of an officer or group of officers belonging to a particular category with reference to a notional date, that will lead to great uncertainty in public service. The date of entry into a particular service was considered to be the most safe rule to follow while determining the inter se (sic) one officer or the other or between one group of officers and the other recruited from the different sources. After referring to different judgments of this Court, a Constitution Bench in the case of Direct Recruit Class II Engineering Officers' Association v. State of Maharashtra, (1980) 2 SCC 715 : (AIR 1990 SC 1607), came to the same conclusion. The same has been reiterated in the case of State of West Bengal v. Aghore Nath Dev,(1993) 3 SCC 371. It is now almost settled that seniority of an officer in service is determined with reference to the date of his entry in the service, which will be consistent with the recruitment of Articles 14 and 16 of the Constitution. Of course, if the circumstances so require a group of persons can be treated a class separate from the rest, for any preferential or beneficial treatment while fixing their seniority. But, whether such, group of persons belong to a special class for any special treatment, in matters of seniority has to be decided on objective consideration and on taking into account relevant factors which can stand the test of Articles 14 and 16 of the Constitution. Normally, such classification should be by statutory rule or rules framed under Article 309 of the Constitution. The far-reaching implication of such rules need not be impressed, because they purport to affect the seniority of persons, who are already in service. For promotional posts, generally the rule regarding merit and ability or seniority-cum- merit is followed in most of the services. As such the seniority of an employee in the later case is material and relevant to further his career, which can be affected by factors, which can be held to be reasonable and rational.