Portability Rule
If you are in the United States and changing from one H-1B employer to another, federal regulations permit you to begin working for the new employer on the start date indicated on the new or concurrent H-1B petition we submitted on your behalf. This is commonly referred to as Portability. 

To verify you qualify for the Portability Rule, a sticker will be placed on your I-797C receipt notice indicating your new work authorization expiration date under the Portability Rule.

Legal citation: 8 CFR 214.2(h)(2)(i)(H)‚Äč