45 CFR §1149.23

1. (a)You may file a motion with the ALJ asking him/her to reopen the case at any time before an initial decision becomes final. The ALJ may only reopen a case if, in this motion, he/she determines that you set forth extraordinary circumstances that prevented you from filing a timely answer. The initial decision will be stayed until the ALJ makes a decision on your motion to reopen. The reviewing official may respond to the motion.
2. (b)If the ALJ determines that you have demonstrated extraordinary circumstances excusing your failure to file a timely answer, the ALJ will withdraw the initial decision and grant you an opportunity to answer the complaint.
3. (c)A decision by the ALJ to deny your motion to reopen a case is not subject to review or reconsideration.