I also am not a tax lawyer. However, at least the NY non-resident form specifies that the tax is only owed on NY sources. Probably, when you are on a work trip, the "source" of your income is still the office you work at in your home state. Also worth noting that if you're only there for a week, you'd have to make a great deal of money annually before you got above the standard deduction cutoff for that state.