I don't know where Maine is getting Resident Permits Only. But we have to go with what they say. As you can see it is the Chief of the State Police who must have made that decision. Here is their law.
Title 25: INTERNAL SECURITY AND PUBLIC SAFETY
Part 5: PUBLIC SAFETY
Chapter 252: PERMITS TO CARRY CONCEALED HANDGUNS
§2001-A. Threatening display of or carrying concealed weapon
A firearm carried by a person to whom a valid permit to carry a concealed firearm has been issued by another state if a permit to carry a concealed firearm issued from that state has been granted reciprocity. The Chief of the State Police may enter into reciprocity agreements with any other states that meet the requirements of this paragraph. Reciprocity may be granted to a permit to carry a concealed firearm issued from another state if:
(1) The other state that issued the permit to carry a concealed firearm has substantially equivalent or stricter requirements for the issuance of a permit to carry a concealed firearm; and
(2) The other state that issued the permit to carry a concealed firearm observes the same rules of reciprocity regarding a person issued a permit to carry a concealed firearm under this chapter; [2011, c. 394, §3 (AMD); 2011, c. 396, §2 (AMD).]
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