Generally speaking, an immigrant should only have one alien number throughout the course of their immigration process and the same alien number should be placed on that applicant’s naturalization certificate. These days, though, there have been some complaints online that applicants will receive one alien number on their employment card and then will receive a completely different alien number on their newly issued green card.
If you receive your green card and you notice that the alien number is a different one than the alien number that was previously issued to you on the employment card, you should take some action to ensure that the mistake is corrected. For instance, you can file a form I-90 and mark that there is a mistake on the green card resulting from USCIS error. In other words, check the box that says that a service error took place. You do Not need to attach a filing fee, but be sure to follow the instructions for the I-90 form.
However, some people do not want to mail in their newly issued green card. As a result, those individuals can write a letter to USCIS and request that the two alien numbers be merged into one file. Be sure to keep a copy of this letter and send it to USCIS via certified mail so that you can keep proof of mailing for your records. Please also call USCIS at 1-800-375-5283 after you mail the letter, to see if any action has taken place on merging your two files. It is best to keep records of your letter to USCIS, though, as you may have no record of the details of your phone call to USCIS.
Until you have a new green card issued with the correct alien number or you have knowledge that the two alien number files have been consolidated, be sure to list all alien numbers on future applications with USCIS, including address changes, for example.