My employer says I have to work 100% remotely to apportion income I earned in Massachusetts when I live in NH. Is that accurate?

[jwads]

I worked in the state 12 days last year and from home the rest of the time. This isn’t elated to the pandemic.

[linear]

That is incorrect. If you were not physically present in MA when working (and were not working remotely due to the pandemic), your income is not considered MA-source income. See:

https://www.mass.gov/service-details/learn-about-massachusetts-gross-income-for-nonresidents

[TomD8]

The income you earned on the 12 days you actually worked in MA is MA-source income, and therefore is taxable by MA.

So you do have to apportion your income accordingly.