DHS regulations currently define the period of an F-1 student's status as the time the student is pursuing a full course of study at an SEVP-certified school or engaging in authorized post-completion OPT. 8 CFR 214.2(f)(5). They do not specify how much time the student may be unemployed, making it difficult to determine when an unemployed student on post-completion OPT violates the requirements for remaining in F-1 status. As status during OPT is based on the premise that the F-1 student is working, the re must be a limit on unemployment, just as the F-1 student's period in school is based on the premise that he is actually pursuing a full-time course of study, and there are limits on how often the student can reduce his course load. An F-1 student who drops out of school or does not pursue a full-time course of study loses status; an F-1 student with OPT who is unemployed for a significant period should similarly put his status in jeopardy. Therefore, this rule specifies an aggregate maximum allowed perio d of unemployment of 90 days for students on 12-month OPT. This maximum period increases by 30 days for F-1 students who have an approved 17-month OPT period. In addition to clarifying the student's status, this measure allows time for job searches or a break when switching employers.

 

Source: http://www.uscis.gov/propub/ProPubVAP.jsp?dockey=ed2d96c7cc8d35f1ec324d6b423cf3d3