Short answer
A small amount from soup is unlikely to cause serious harm, but watch for signs of salt poisoning like excessive thirst, vomiting, or diarrhea. Deli meat is high in salt and preservatives, which aren't good for dogs. Offer fresh water, and call your vet if you notice any unusual behavior or stomach upset.
Deli meat — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Salt and preservatives, and some are seasoned with garlic. A small piece as a treat.
The full verdict, portion guidance and serving notes are collected on the Deli meat food facts page.