State tax filing

Mass must withhold income tax for any business performed within Mass, they are getting more like NY.If you're a non-Massachusetts employer who conducts business or maintains an office in Massachusetts, you must withhold the amount determined for Massachusetts income tax purposes, minus any amount deducted and withheld for your own state. If there's no state withholding in your business's home state, you must withhold and send to us the full amount determined for Massachusetts purposes. Whether the employee works on the road, at home or in an office maintained by you, the employer, does not affect your withholding obligation. <a rel="nofollow" target="_blank" href="https://www.mass.gov/guides/withholding-taxes-on-wages">https://www.mass.gov/guides/withholding-taxe...>

CT;  The employer will withhold tax for the state in which the individual works and will submit the tax to that state.  If the employer is also registered to withhold Connecticut income tax, Connecticut income tax must be withheld by the employer, but only to the extent that Connecticut income tax withholding exceeds the amount required to be withheld for the state in which the services are performed. For further information, employers should consult the Circular CT, Connecticut Employer's Tax Guide  (so if CT tax rate is higher only then CT taxes must be withheld.  Connecticut has a progressive income tax structure, with rates ranging from 3 percent to as high as 6.99 percent, while Massachusetts has a flat 5.15 percent income tax rate so depending on income will depend if CT tax should be paid ).
Determining How Much to Withhold From Nonresident Employees Who Work Partly Within and Partly Outside Connecticut . . . page 12  
<a rel="nofollow" target="_blank" href="https://portal.ct.gov/-/media/DRS/Publications/pubsip/2018/IP-2018(1).pdf?la=en">https://portal.ct.g...>