Under well established Supreme Court precedent and by statute, Defendant may collaterally attack his removal order. United States v. Mendoza-Lopez, 481 U.S. 828 (1987); 8 U.S.C. 1326(d). In Mendoza-Lopez, two defendants challenged their 1326 indictments because the immigration judge overseeing the defendants' deportation (removal) proceedings failed to inform the defendants of their right to relief from deportation and accepted unconsidered waivers of appeal. In reviewing the defendants' challenge to their removal order, the Supreme Court held that due process required that persons accused of illegal reentry be afforded the opportunity to challenge their removal/deportation orders in their criminal proceedings because "where the defects in an administrative proceeding foreclose judicial review of that proceeding, an alternative means of obtaining judicial review must be made available before the administrative order may be used to establish conclusively an element of a criminal offense." Id. at 838. The Court concluded that both defects in the defendants' deportation proceedings, that is the misinformation provided by the immigration judge regarding the defendants' eligibility for relief from deportation and their unconsidered waivers of the right to appeal, constituted due process violations because separately each violation "amounted to a complete deprivation of judicial review" of their deportability. Id. at 840 ("If the violation of respondents' rights that took place in this case amounted to a complete deprivation of judicial review of the determination [of deportability], that determination may not be used to enhance the penalty for an unlawful entry under 1326.").



Subsequently, the Fifth Circuit interpreted Mendoza-Lopez to require defendants challenging their deportation (removal) orders in 1326 prosecutions to establish the following: "1) the prior hearing was 'fundamentally unfair;' 2) the hearing effectively eliminated the right of the alien to challenge the hearing by means of judicial review of the order; and 3) the procedural deficiencies caused the alien actual prejudice." U.S. v. Mendoza-Mata, 322 F.3d 829, 832 (5th Cir. 2003). Prejudice is established where the defendant can show that "there was a reasonable likelihood that but for the errors complained of the defendant would not have been deported." Id. If the noncitizen was removable but, as a result of the INS' errors, the proceeding would have yielded different results, the removal order is not valid for purposes of 1326. Id. ("if the defendant was legally deportable and, despite the INS' errors, the proceeding 'could not have yielded a different result,' the deportation is valid for purposes of section 1326.").
Thanks to Javier Maldonado.