Your tree has cedar-hawthorn rust. It's a fungi that requires two hosts for its lifecycle, the eastern red cedar and other junipers then the trees in the Rosaceae family of which the hawthorn is one member. Somewhere within a hundred feet of your hawthorn is a juniper or eastern red cedar that will have different looking galls that are part of the fungal cycle.

If there is little to no leaf loss, it won't harm your tree even though up close it may be unsightly. You can also try to break the cycle by looking for the brown woody galls on your junipers and eastern red cedar plants to break the cycle.

Here is a full article on the lifecycle and management of this fungal disease that I'm sure will be of significant help. It has photos of the galls so you'll know that to look for.  Understanding the lifecycle of this rust disease for timing purposes and looking for those galls if they're on your property should help.

https://extension.umn.edu/plant-diseases/cedar-apple-rust#managing-rust-on-apples%2C-hawthorns%2C-an...

I hope this information helps.