Gun tax in Maine?

"A gun and ammunition tax that would create a fund to increase security at the state's courthouses has been proposed by several members of the Legislature's Judiciary Committee. The 7 percent tax would be in addition to the 5 percent state sales tax that consumers already pay when they buy guns and ammunition from licensed dealers in the state. . . . Entry screening is conducted an average of 10 days each year for each of the state's 41 courthouses, she said. The chief justice also told the Legislature that during that limited time screeners had confiscated more than 1,400 knives or related weapons and five firearms."

Possibly a knife tax would make more sense? In any case, while I am open to argument, it is not clear to me how a gun and bullet tax can be any more constitutional than a newspaper tax.