29 USC 1203 - Procedures in connection with prohibited transactions

(a) Notification to Secretary of Labor; opportunity to comment on imposition of tax under section 4975 of title 26; waiver; requests for investigations 
Unless the Secretary of the Treasury finds that the collection of a tax is in jeopardy, in carrying out the provisions of section 4975 of title 26 (relating to tax on prohibited transactions) the Secretary of the Treasury shall, in accordance with the provisions of subsection (h) of such section, notify the Secretary of Labor before sending a notice of deficiency with respect to the tax imposed by subsection (a) or (b) of such section, and, in accordance with the provisions of subsection (h) of such section, afford the Secretary an opportunity to comment on the imposition of the tax in any case. The Secretary of the Treasury shall have authority to waive the imposition of the tax imposed under section 4975 (b) in appropriate cases. Upon receiving a written request from the Secretary of Labor or from the Pension Benefit Guaranty Corporation, the Secretary of the Treasury shall cause an investigation to be carried out with respect to whether the tax imposed by section 4975 of title 26 should be applied to any person referred to in the request.
(b) Consultation 
The Secretary of the Treasury and the Secretary of Labor shall consult with each other from time to time with respect to the provisions of section 4975 of title 26 (relating to tax on prohibited transactions) and with respect to the provisions of subchapter I of this chapter relating to prohibited transactions and exemptions therefrom in order to coordinate the rules applicable under such standards.
(c) Transmission of information to Secretary of the Treasury 
Whenever the Secretary of Labor obtains information indicating that a party-in-interest or disqualified person is violating section 1106 of this title, he shall transmit such information to the Secretary of the Treasury.