G.R. No. 212719 - Inmates of the New Bilibid Prison vs. De Lima

On June 6, 2013, Republic Act No. 10592 amended Articles 29, 94, 97, 98, and 99 of the Revised Penal Code (RPC), enhancing good conduct time allowance (GCTA), time allowance for study, teaching and mentoring (TASTM), and special time allowance for loyalty (STAL).
On March 26, 2014, the Department of Justice (DOJ) and the Department of the Interior and Local Government (DILG) promulgated the Implementing Rules and Regulations (IRR) effective April 18, 2014; Section 4, Rule I mandated that GCTA, TASTM, and STAL be applied prospectively.

G.R. No. 212719 (Roxas et al.): Filed June 18, 2014 by inmates of New Bilibid Prison challenging the IRR’s prospectivity; interventions by Atty. Saguisag (July 2014) and FLAG (Montinola et al., October 2014).
G.R. No. 214637 (Edago et al.): Filed October 24, 2014 by Maximum Security inmates likewise assailing Section 4, Rule I as contrary to RPC Article 22, and violating equal protection and due process.

The Supreme Court consolidated the two cases (June 16, 2015), received comments from the Office of the Solicitor General, and admitted replies from intervenors.
The sole issue became the legality of Section 4, Rule I of the IRR and its prospective application of statutory time allowances.

Whether there is an actual case or controversy and petitioners have standing under Supreme Court precedents.
Whether certiorari and prohibition are proper remedies and whether hierarchy-of-courts rules bar direct resort to the Supreme Court.

Whether Section 4, Rule I of the IRR, mandating prospective application of GCTA, TASTM, and STAL, is valid.
Whether that provision violates RPC Article 22 on retroactivity of penal laws and the constitutional due process and equal protection guarantees.