Technically I think the label should say "Made in the USA with imported tags" but, I doubt you would be in trouble for leaving that last part off. Here are the official rules from the FTC. Go to Page 20 specifically.
The "Made in USA" country of origin requirement on the label is where the garment was constructed, not the labels themselves.So I'm printing on AA shirts which are obviously made in America. I'm also printing the shirts in the great smelly state of New Jersey... However, the labels that I'm adding (purely decorative non-informative) to the bottom of my shirt with my logo are coming from Lucky Label in Bangkok...
Is it illegal to say Made In USA??