Share your insights or perspective on the financial matter presented in the input.

What is a “margin-call” and how are they enforced?
If you don't have a margin account, then you will not have margin calls. You need a margin account if you wish to "buy on margin", to sell stocks "short", or to sell options, or maybe some other esoteric things I have not thought of.  If you don't do those things, then you do not need a margin account and will not get margin calls. In your example, it doesn't sound like margin has been used, If you deposit $20 and used it to buy $20 of stock and it then falls to $5, "they" did not lose the money, you did.  But if no margin was used, then no margin call would result.