Alito, J., dissenting
discretion when it comes to the arrest and release of criminal aliens.” Nielsen v. Preap, 586 U. S. ___, ___ (2019) (slip op., at 15) (emphasis in original).
Two such limits are important here. First, 8 U. S. C. §1226(c) directs the Government to “take into custody any alien” inadmissible or deportable on certain criminal or terrorist grounds “when the alien is released” from criminal custody, including when such an alien is released on “parole, supervised release, or probation.” Second, §1231(a) imposes a categorical detention mandate. Section 1231(a)(2) provides that the Government “shall detain [an] alien” “[d]uring the removal period,” which often begins either when an “order of removal becomes administratively final” or when an “alien is released from detention or confinement” not arising from immigration process, §1231(a)(1)(B). This requirement is reinforced by the direction that “[u]nder no circumstance during the removal period shall the [Government] release an alien” found inadmissible or deportable under almost any of the grounds relevant under §1226(c). §1231(a)(2). And §1231(a)(1)(A) commands that the Government “shall remove the alien” within the removal period.
All of our recent decisions interpreting these provisions confirm that, for covered aliens, shall means shall; it does not mean “may.” See Johnson v. Guzman Chavez, 594 U. S. ___, ___–___, and n. 2 (2021) (slip op., at 2–3, and n. 2); Nielsen, 586 U. S., at ___–___ (slip op., at 16–17). Until quite recently, that was the Government’s understanding as well. See Biden v. Texas, 597 U. S. ___, ___–___ (2022) (slip op., at 8–9) (Alito, J., dissenting).
Actions taken by Congress when IIRIRA was enacted underscore this conclusion. Because the provisions described above left the Executive with no discretion to refrain from arresting and detaining covered aliens, even during the time immediately after IIRIRA’s enactment when the Executive was still “expand[ing] its capacities” to enforce the
