This has nothing to do with unions. Nothing at all.
On a per capita income basis, Massachusetts taxes are LOWER than in such right-to-work states as Georgia and North Carolina.
Right-to-work states are generally states with lower educational levels than northern states, so they need every advantage they can get to close the gap. It helps a little bit, until companies realize they can get low-skilled workers even cheaper than what Mississippi offers if they go to a foreign country.