Since you live and work in Maryland, all your income is subject to Maryland tax, no matter where the income is from. If you work only in Maryland, and never come to New Jersey, you should have Maryland tax withheld and not New Jersey tax. If you are working in Maryland, it doesn't matter that you are working for a company that is located in New Jersey. You would not have to pay any New Jersey tax or file a New Jersey tax return.
However, if you occasionally work in New Jersey, even if only for a few days here and there, the income you earn for the time that you work in New Jersey is New Jersey income and is subject to New Jersey tax. You would have to file a New Jersey nonresident tax return in addition to your Maryland resident tax return. So you might want to have New Jersey tax withheld only for the days that you work in New Jersey. You will get a credit on your Maryland tax return for part or all of the tax that you pay to New Jersey. Prepare your New Jersey nonresident tax return first, then your Maryland resident tax return, to make sure that the credit is calculated correctly.
This information applies to the specific states that you asked about. The situation would be similar for most other states, but a few states have different rules for telecommuters or for people who live in one state and work in another.
