What is a priority date?

If your category is employment-based and requires a labor certification, the priority date is established on the date a labor certification is filed with the U.S. Department of Labor. If your category is employment-based but does not require a labor certification, then the priority date is established on the date the USCIS receives the I-140 Immigrant Visa Petition. However, in either situation the priority date does not attach to your case until the I-140 Immigrant Petition has been approved.