533US2 688 Unit: $U87 [10-21-02 18:35:10] PAGES PGT: OPIN ZADVYDAS v. DAVIS Opinion of the Court able”; it does not deprive an alien of the right to rely on 28 U. S. C. § 2241 to challenge detention that is without statutory authority. Another provision, 8 U. S. C. § 1252(a)(2)(B)(ii) (1994 ed., Supp. V), says that “no court shall have jurisdiction to review” decisions “specified . . . to be in the discretion of the Attorney General.” The aliens here, however, do not seek review of the Attorney General’s exercise of discretion; rather, they challenge the extent of the Attorney General’s authority under the post-removal-period detention statute. And the extent of that authority is not a matter of discretion. See also, e. g., § 1226(e) (applicable to certain detentionrelated decisions in period preceding entry of final removal order); § 1231(a)(4)(D) (applicable to assertion of causes or claims under § 1231(a)(4), which is not at issue here); §§ 1252(a)(1), (a)(2)(C) (applicable to judicial review of “final order[s] of removal”); § 1252(g) (applicable to decisions “to commence proceedings, adjudicate cases, or execute removal orders”). We conclude that § 2241 habeas corpus proceedings remain available as a forum for statutory and constitutional challenges to post-removal-period detention. And we turn to the merits of the aliens’ claims. III The post-removal-period detention statute applies to certain categories of aliens who have been ordered removed, namely, inadmissible aliens, criminal aliens, aliens who have violated their nonimmigrant status conditions, and aliens removable for certain national security or foreign relations reasons, as well as any alien “who has been determined by the Attorney General to be a risk to the community or unlikely to comply with the order of removal.” 8 U. S. C. § 1231(a)(6) (1994 ed., Supp. V); see also 8 CFR § 241.4(a) (2001). It says that an alien who falls into one of these cate-