What matters should be your residence and your employer location. It seems that 新澤西州的中國人辦的中介公司 is your employer instead of the company in MA.
- If you reside in NJ and get paid by 新澤西州的中國人辦的中介公司, your withholding should be with NJ rate.
- If you reside in MA and get paid by 新澤西州的中國人辦的中介公司, you may be subject to withholding with rate of either state.
It seems that NJ company treats you as a MA resident. I am no PR expert, just my opinion.
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As a New Jersey employer, you are required to withhold New Jersey income tax from wages paid to all New Jersey residents unless you are withholding another jurisdiction's income tax at a rate equal to or greater than New Jersey's rate. You must also withhold New Jersey income tax for nonresident employees physically working in this State. Pennsylvania residents are the only out-of-state residents exempt from New Jersey withholdings. As a result of the Reciprocal Income Tax Agreement between New Jersey and Pennsylvania, compensation earned in New Jersey by a Pennsylvania resident is not subject to New Jersey Gross Income Tax. If you employ a Pennsylvania resident in New Jersey, that employee should complete an Employee's Certificate of Non-residence in New Jersey (Form NJ-165) and file it with you. Once an employee has provided you with a completed Certificate of Non-residence you must stop withholding New Jersey income tax.
http://www.state.nj.us/treasury/taxation/njit30.shtml
