New Delhi: The Centre has opposed a petition in the Supreme Court seeking an income-based sub-quota within reserved categories, arguing that reservation for Scheduled Castes (SCs), Scheduled Tribes (STs) and Other Backward Classes (OBCs) is based on historical and social backwardness rather than economic status.In a counter-affidavit filed by the Department of Social Justice and Empowerment, the government said the petition sought judicial directions to frame reservation policy, a matter that falls within the executive's domain and cannot be mandated through a writ of mandamus. On the question of extending the creamy layer principle, which excludes the economically advanced among OBCs, to SCs and STs, the Centre relied on the nine-judge ruling in the Indra Sawhney case.Read more: Centre opposes 'creamy layer' for SC/ST reservation in Supreme Court, citing legal precedentThe government said the judgment made it clear that the discussion on excluding the socially advanced was "confined to OBCs only and has no relevance in the case of SC/STs". It also cited a Constitution bench judgment which held that the creamy layer principle does not apply to SCs and STs.The petition seeks directions to the Centre to introduce a more equitable reservation system based on a merit-cum-means approach instead of the existing framework. It also seeks income-based preferences within each reserved category so that economically weaker candidates among SCs, STs, OBCs and the Economically Weaker Sections are treated as a distinct sub-class and given higher priority in selection.Read more: Supreme Court says SC, ST, OBC and Economically Weaker Sections entitled to general category post if...The Centre argued that any change to the policy, particularly the introduction of income-based preferences within reserved categories, would require a comprehensive review supported by empirical and socio-economic data.