All variances granted pursuant to this part shall have only future effect. In his discretion, the Assistant Secretary may decline to entertain an application for a variance on a subject or issue concerning which a citation has been issued to the employer involved and a proceeding on the citation or a related issue concerning a proposed penalty or period of abatement is pending before the Occupational Safety and Health Review Commission or appropriate State review authority until the completion of such proceeding.
29 C.F.R. §1905.5