20 CFR §404.999b

1. (a)The following individuals may be reimbursed for certain travel expenses—
   1. (1)You, when you attend medical examinations upon request in connection with disability determinations; these are medical examinations requested by the State agency or by us when additional medical evidence is necessary to make a disability determination (also referred to as consultative examinations, see § 404.1517);
   2. (2)You, your representative (see § 404.1705 (a) and (b)), and all unsubpoenaed witnesses we or the State agency determines to be reasonably necessary who attend disability hearings; and
   3. (3)You, your representative, and all unsubpoenaed witnesses we determine to be reasonably necessary who attend hearings on any claim for benefits before an administrative law judge.
2. (b)Sections 404.999a through 404.999d do not apply to subpoenaed witnesses. They are reimbursed under §§ 404.950(d) and 404.916(b)(1).