mecklenburg

Probably not. Fungi get their nourishment from decaying material found in most soils.

Why does the tomatoe start rottening before they are done growing?

The mushrooms themselves aren't a problem, but they are probably a sign that the soil is too wet. That's going to make the roots rot.

If the leaves are yellow or droopy, then you definitely have a problem with too much water. Make sure that you have good drainage in your container, and plenty of sun.

So I'm growing deck tomatoes and recently noticed underneath the plants there yellow mushrooms sprouting up, could these potentially hurt my plants?