Extending Your Stay
U nonimmigrants are required to have approval from the U.S. Citizenship and Immigration Services (USCIS) Vermont Service Center to stay beyond the date indicated on their admission stamp or paper Form I-94. To receive an extension of U nonimmigrant status, a U nonimmigrant must file a Form I-539, Application to Extend/Change Nonimmigrant Status. See page 8 of the USCIS Policy Memo PM-602-0032.1 on the USCIS website for more guidance.
You must depart the United States on or before the date indicated on your admission stamp or paper Form I-94, unless your request to extend your stay is approved by USCIS.
Failure to depart the United States on time will result in you being out of status. Under U.S. law, visas of travelers who are out of status are automatically voided (section 222(g) of the Immigration and Nationality Act). If you had a multiple-entry visa and it was voided due to you being out of status, it will not be valid for future entries into the United States.