The state of Maine already has some of the most restrictive laws about bait fish that you'll find anywhere in the US, but according to this article from the Portland Press Herald, there's an effort underway to go even further.
Currently Maine uses a whitelist to regulate bait fish. You can't imported them into the state, so the only way to get bait fish is to either catch them yourself or buy them from suppliers that are either catching them fresh or catching and raising them from in-state stock. Only the following 23 species are allowed to be used as bait: Smelt, Lake chub, Eastern silvery minnow, Golden shiner, Emerald shiner, Bridle shiner, Common shiner, Blacknose shiner, Spottail shiner, Northern redbelly dace, Finescale dace, Fathead minnow, Blacknose dace, Longnose dace, Creek chub, Fallfish, Pearl dace, Banded killifish, Mummichog, Longnose sucker, White sucker, Creek chubsucker, American eel, and Blackchin shiner. That's pasted directly from the government website, no scientific names and no discernible order as far as I can tell. They also have a few illustrations here.
Bill LD 163, introduced by state lawmaker Rep. Thomas Watson (D) of Bath, ME would ban the use of the following four species currently on the list: Eastern silvery minnow, Emerald shiner, Spottail shiner, and Blackchin shiner. The concern is that there is a danger of those species becoming established and threatening native fish species. Seems like a good idea, but if you read the article, the director of the state's Department of Inland Fisheries and Wildlife notes that it is difficult to positively identify different species of bait fish, and that distinguishing between minnow species often requires laboratory work. Sounds like banning some minnows and allowing others doesn't really make sense from a practical standpoint. Furthermore, according to the DIFW it is not even clear whether the species proposed to be banned are native or introduced in Maine. So, then how did this bill even get off the ground? Unfortunately, I cannot find any background information to understand its origin - the bill text is simply a list of bait fish with the "bad" ones crossed off.