Yes it could. It could also just spend the bitcoins in its possession (people won't see it any different than a normal withdrawal). Mints obviously require you to trust them. They have custody over your bitcoin.
On a side note since deposits and withdrawals are completely anonymous, they cannot selectively stop specific participants from doing these things.
they cannot selectively stop participants from [depositing and withdrawing]
They can. I outline how in this post: #565618
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