8 C.F.R. § 204.304
(a) Prohibited payments. Neither the applicant/petitioner, nor any individual or entity acting on behalf of the applicant/petitioner may, directly or indirectly, pay, give, offer to pay, or offer to give to any individual or entity or request, receive, or accept from any individual or entity, any money (in any amount) or anything of value (whether the value is great or small), directly or indirectly, to induce or influence any decision concerning:
(b) Permissible payments. Paragraph (a) of this section does not prohibit an applicant/petitioner, or an individual or entity acting on behalf of an applicant/petitioner, from paying the reasonable costs incurred for the services designated in this paragraph. A payment is not reasonable if it is prohibited under the law of the country in which the payment is made or if the amount of the payment is not commensurate with the costs for professional and other services in the country in which any particular service is provided. The permissible services are: