Unfortunately I am not an accountant and cannot give you tax advise, however, NJ has a non-resident income tax form, which you may be required to file: https://www.state.nj.us/treasury/taxation/taxtables.shtml

Edit to add: According to my interpretation of this: https://www.state.nj.us/treasury/taxation/pdf/current/1040nr...

Assuming your income is over $20,000, you ARE required to file a NJ state tax return.

Also, note that even if you don't file a tax return, doesn't mean you are exempted from doing so.

Example, as a citizen of Texas, you are also required to pay use tax on any items aquired out of state/country and used in the state. My assumption is that you don't also pay that either, even thought you are legally required to do so. It turns out that use Tax is particularly difficult to audit and collect for, especially without a mandatory return like state income tax.

I had a paid remote internship for about 6 months for a Texas company while I lived in Missouri. I had to file a Texas state income tax form, or at least my reading of the law indicated that I had to, and Texas gladly took the money.

From where did you get a form that doesn't exist? Texas has no income tax.

Perhaps the Texas company sent him the form for MO, as they DO have state-income tax.

Agreed. I see no exemption there for “I was just attending a conference and just stayed in a hotel for a few days.” Much less spending weeks at a remote company location or job site.

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.

Apparently you technically should, but you aren't expected to because it would be impractical.

https://en.wikipedia.org/wiki/Jock_tax

If you’re doing client work there — and you may not be! —- you’re responsible for the portion of the income earned in that state (you have “nexus,” in the parlance — I’m less sure about merely having presence in a state even if the work isn’t generating company income, but in some cases I think that’s treated as nexus as well). In those cases, your company should send you state W-2s for your income; most decent consulting firms offer tax prep services if you end up working in a lot of state and international jurisdictions with tax consequences.