I-140 petition must be approved; and
To qualify for AC21 portability, a foreign national must be the beneficiary of an APPROVED labor certification application (stage 1 of the green card process), and an APPROVED I-140 petition (stage 2 of the green card process). Documentation of an approved I-140 is met by having a copy of the I-140 petition approval notice. Some people are tempted to change employers with an I-485 application pending 180 days and a pending I-140 (rather than approved I-140). This would be extremely risky and is not recommended.
I-485 application must be pending over 180 days; and
In addition to an approved I-140, to qualify for AC21 portability, a foreign national's I-485 application must be pending over 180 days. The I-485 is the 3rd/final stage of the green card process. Documentation of the I-485 application pending over 180 days is also potentially met by having a copy of the I-485 receipt notice; however, sometimes calculating the number of days an I-485 application has been pending can be complicated, particularly for individuals who filed I-485 applications in July 2007 or early August 2007, because USCIS received a record number of I-485 filings during that period and I-485 receipt notices often fail to list the correct date. In general, the date that the I-485 application arrived at USCIS should be considered the "received date" and that date should count as day 1 in calculating the 180 days.
New employment must be within the "same or similar" occupational classification.
In addition to having an approved I-140 petition and I-485 application pending 180+ days, to qualify for AC21 portability, the foreign national must have a new position which is within the "same or similar" occupational classification. USCIS has not provided regulations on this issue, but it is generally felt that "same or similar" occupational classification ties to the US Dept of Labor's job classification listed on the labor certification application, which should also correspond to a job code listed on the I-140 petition. Sometimes this analysis is very straightforward; but it can often be complicated. One recurring issue relates to a technical employee who is now eligible for a managerial position. The managerial position could arguably be in a different job classification and may not qualify under AC21 portability.
If you use AC21 portability, updating USCIS is recommended.
If a foreign national does take advantage of AC21 portability and changes employment, then USCIS recommends that the individual update the USCIS office where the I-485 application is pending. Normally the update would include a letter from the individual (or preferably the new employer) attesting to the new position, with a discussion of the new job and how it is within the same or similar occupation as the prior labor certification and I-140. Further, the AC21 portability filing should include documentation that the sponsored foreign national did work for the initial sponsoring company for the first 180 days the I-485 application was pending. Useful documentation on this issue could include payroll records and W-2s from the initial sponsoring employer.
Remember Form AR-11 if you move.
If, as a result of new employment, the foreign national moves to a new home address, then the foreign national must update USCIS of his or her new address, using Form AR-11, found at www.uscis.gov. Be sure to update USCIS for all family members with I-485 applications pending, as USCIS does mail notices directly to home addresses in the I-485 process, including eventually the I-551 permanent resident card. IMPORTANTLY, USCIS has a special (and somewhat annoying) arrangement with the US Post Office so that even if a foreign national tells the post office that he has moved, the Postal Service is PROHIBITED from forwarding mail sent by USCIS. This creates a lot of problems for people who do not know this rule.
Finally - Consider who filed a G-28 (attorney representation form).
Finally, consider who filed a G-28 for the pending I-485 application. If the G-28 attorney representation form was filed by your initial employer's attorney, then any RFE (Request for Evidence) on the pending I-485 will be sent to your employer's attorney. Even if you change employers, USCIS will still consider that initial attorney as your attorney. Thus, it may be useful to retain an independent attorney, or use your new employer's lawyer.