Per IRS Instructions for Form 1040-NR U.S. Nonresident Alien Income Tax Return on page 7 (click the link and view the entire publication for additional details regarding the items below):
Who Must File Form 1040-NR
You must file Form 1040-NR if any of the following conditions apply to you.
Exceptions. You do not need to file Form 1040-NR if you meet (1) or (2) below.
To determine if you need to file Form 1040-NR:
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.