"If the extent of reservation goes beyond cut-off point then it results in reverse discrimination. Anti-discrimination legislation has a tendency of pushing towards de facto reservation.

"Therefore, a numerical benchmark is the surest immunity against charges of discrimination," a five-judge constitution Bench headed by Chief Justice Y K Sabharwal, said in a judgement which held that the creamy layer within the Scheduled Castes and Scheduled Tribes should be kept out of the benefit of quotas in government jobs and promotions.

Maintaining that though it was the discretion of the state government concerned to provide quota subject to the existence of "backwardness" and "inadequacy of representation" in public employment, the Bench said "reservation has to be used in a limited sense otherwise it will perpetuate casteism in the country".

The court said in order to ascertain whether a given class or group was adequately represented in the service or not, "government has to apply the cadre strength as a unit in the operation of the roster".

"The cadre strength as a unit also ensures that upper ceiling limit of 50 per cent is not violated. Further, the roster has to be post specific and not vacancy based."

The court held that the backlog vacancies couldn't be carried forward for indefinite period and "the appropriate government will now have to introduce the time-cap depending upon the fact situation".

Elaborating further, the court said in working out the carry-forward rule, two factors need to be kept in mind, namely the unfilled vacancies and the time factor and this needs to be explained.

"On one hand of the spectrum, we have unfilled vacancies; on the other hand, we have a period spread over a number of years over which unfilled vacancies are sought to be carried over.

"These two are alternating factors and, therefore, if the ceiling limit on the carry-over of unfilled vacancies is removed, the other alternative time-factor comes in and in that event, the time scale has to be imposed in the interest of efficiency in administration as mandated by Article 335," the Bench said.

It said if the time-scale was not kept then posts will continue to remain vacant for years, which would be detrimental to the administration.

The court said while extending the policy of reservation Article 335 was to be read with Article 46 which provides that the state should promote with special care the educational and economic interest of the weaker section of the people and in particular of the SCs and STs and protect them from social injustice.

"Therefore, where the state finds compelling interests of backwardness and inadequacy, it may relax the qualifying marks for SCs and STs. These compelling interest however have to be identified by weighty and comparable data," the apex court said.