49 CFR 670.21: General.

In addition to actions described in §§ 670.23 through 670.29, in exercising his or her authority under this part, the Administrator may—

(a) Require more frequent oversight of a recipient by a State Safety Oversight Agency that has jurisdiction over the recipient;

(b) Impose requirements for more frequent reporting by a recipient;

(c) Order a recipient to develop and carry out a corrective action plan; and

(d) Issue restrictions and prohibitions, if through testing, inspection, investigation, audit or research carried out under Chapter 53, the Administrator determines that an unsafe condition or practice, or a combination of unsafe conditions and practices, exist such that there is a substantial risk of death or personal injury.