28 CFR 21.3: Aliens.
The following aliens are entitled to witness fees and allowances provided in § 21.4:
(1) Aliens lawfully admitted for permanent residence (documentary evidence: Form I-151 or Form 1-551, Alien Registration Receipt Card);
(2) Aliens lawfully admitted in one of the nonimmigrant categories described in 8 U.S.C. 1101(a)(15) (documentary evidence: unexpired Form 1-94, Arrival-Departure Record). But see below § 21.3(b);
(3) Aliens admitted as refugees under 8 U.S.C. 1157 and aliens granted asylum under 8 U.S.C. 1158 (documentary evidence: Form I-94, Arrival Departure Record, indicating admission as refugee under 8 U.S.C. 1157 or granting asylum under 8 U.S.C. 1158, employment authorized);
(4) Aliens who have rendered themselves amenable to deportation proceedings, but have not admitted deportability or have not been determined to be deportable pursuant to section 242 of the Immigration and Nationality Act (8 U.S.C. 1252).
An alien who is “excludable” in accordance with 8 U.S.C. 1226, but whose removal is stayed by the Attorney General (in accordance with 8 U.S.C. 1227(d)) because:
(1) The testimony of the alien is necessary on behalf of the United States in the prosecution of offenders against the United States, or
(2) The testimony of the alien is necessary on behalf of an indigent criminal defendant in accordance with Rule 17(b) of the Federal Rules of Criminal Procedures,
is entitled to a $1 per day witness fee. No other fees and allowances are authorized.
An alien who has been paroled into the United States for prosecution pursuant to 8 U.S.C. 1182(d)(5) (documentary evidence: Form I-94, Arrival-Departure Record, Parole Edition), or an alien who has admitted belonging to a class of aliens who are deportable, or an alien who has been determined pursuant to 8 U.S.C. 1252(b) to be deportable (documentary evidence: decision by a Special Inquiry Officer, Board of Immigration Appeals, or court), is prohibited from receiving fees and allowances in accordance with 28 U.S.C. 1821(e).
If the Immigration and Naturalization Service advises that the alien has admitted deportability, or that he or she was paroled into the United States for prosecution, or that deportation proceedings have been completed against the alien with a result favorable to the Government, no payment under 28 U.S.C. 1821 may be made.