Is Walmart inventing their own gun laws??

[grinr]

Seen this sign posted on the ammunition case at my local Walmart.(Deerfoot Meadows Calgary next to WSS)
Can somebody please explain what "ML" refers to,and if it refers to Muzzle Loader(?) just wutdahell exactly is a Muzzleloader licence and since when do I need to show anything to buy black powder or any other reloading components for that matter?
Is this some new law I'm not aware of or just Walmart policy and yet another reason to hate Walmart??
.......not that any Walmart that I'm aware of stocks real BP,roundballs,or any other traditional ML gear that I'd be interested in anyhow...