@DonnaBear65 generally IRS holds that back pay is taxable in the year when received. However, if you received the back pay during NRA status, this back pay from foreign source would not be included in your US income -- depends on your own tax status ( NRA or Resident for Tax purposes ) and when the back-pay is constructively received. Note that as H1-B worker, if you meet the Substantial Presence during the year, then your first day of residency status is the first day you were legally present in the US.
Does this help ? Is there more I can do for you ?
