It is not a problem as long as these two scenarios are followed. First of all you could be working in location X and the PERM is filed for location Y as long as you have the intention to join the location Y you can file even though you are currently working at location X.
The interesting thing is once the I-485 is filed and the I-140 is approved after 180 days of the I-485 you can choose to be wherever you want to be because you are allowed to port your green card. The only requirement is when you start the PERM. File the I-140 and the I- 485. Your intention throughout was to work at location Y but after 180 days if the intention changes it is absolutely no problem.
The second scenario which is very common is when you have consulting jobs and you could be moving from a month to a year with no predictability where you are going to be, it is normally recommended and legally allowed to file the PERM application as though your job is located in the corporate headquarters or principal place of business. More...
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