An I-797 Notice of Action is a form issued by United States Citizenship and Immigration Services when an O-11-129 or H-1 petition for a non-immigrant worker is approved, says Columbia University. The I-797 Notice of Action provides the effective dates of validity.
According to Columbia University, an I-797 Notice of Action also indicates whether a change of status or extension of status has been approved, or whether the consulate listed on the petition has been notified. This one-page form is also sent out by the USCIS to communicate information related to notices or receipt, rejection, reopen, transfer and appointments. USCIS advises people receiving the I-797 Notice of Action to pay close attention to individual details and instructions to avoid case delays.