Facts: These civil appeals arose from arbitral awards concerning the interpretation and implementation of the Building and Other Construction Workers (Regulation of Employment and Conditions of Service) Act, 1996 (BOCW Act) and the Building and Other Construction Workers' Welfare Cess Act, 1996 (Cess Act). The National Highways Authority of India (NHAI) disputed the applicability of these Acts as "subsequent legislation" to contracts entered into with various contractors. The arbitral tribunals had generally ruled in favor of the contractors, deeming the Acts as subsequent legislation.Procedural Posture: Prakash Atlanta (JV) filed one civil appeal, while NHAI filed the other five. The appeals challenged the arbitral awards passed under the Arbitration and Conciliation Act, 1996. The High Court had largely upheld the arbitral awards against NHAI. The Supreme Court was hearing appeals against the High Court orders.Issue: The primary issue was whether the BOCW Act and the Cess Act could be treated as "subsequent legislation" under the contracts between NHAI and its contractors, and whether the arbitral tribunals' interpretation of the contracts was correct. A related issue was whether the absence of constituted Welfare Boards at the time of contract execution affected the applicability of the Cess Act.Holding: The Supreme Court dismissed NHAI's appeals, holding that the arbitral tribunals' interpretation of the contracts was plausible and not patently illegal. The Court emphasized that the constitution of Welfare Boards was a prerequisite for the effective implementation of the BOCW Act and the Cess Act. In the case of Prakash Atlanta (JV), the Court ruled that it was not liable to pay cess retrospectively, setting aside the High Court's order.Reasoning: The Court reasoned that the contractors could not have factored in the cess in their bids if the relevant machinery for its levy and collection was not in place at the time of bidding. The Court emphasized that the constitution of Welfare Boards was a "sine qua non" for giving effect to the BOCW Act and the Cess Act. The Court also noted that NHAI had not raised the issue of cess recovery during the initial arbitration proceedings with Prakash Atlanta (JV), indicating it was an afterthought. The Court reiterated that it would not interfere with plausible interpretations of contract terms by arbitral tribunals, absent perversity or patent illegality. The Court also observed that the ultimate obligation to bear the cess lies with the 'employer' as defined in the BOCW Act.