Your employer can withdraw your i140 once you leave them. USCIS allows porting your green card priority date to a new employer with a new AC21 rule modification done in Jan 2017. Your i140 stays valid if it has not been withdrawn by the employer within 180 days after its approval. You can use the withdrawn i140 as many times as you want to extend or transfer your H1B. USCIS only revokes i140 if they find fraud or misrepresentation by your employer after 180 days. You cannot use the i140 if it has been revoked. Employers may request the i140 withdrawal even after 180 days. Do not worry if the USCIS case status shows as ‘withdrawn’ online. You can use the withdrawn i140 to port your date and extend H1B.