I don't know how the process works with a work visa, but from how he explained it, he worked in the States for a company that invited him to come on a work visa (constructon), and when he returned to Bosnia and quit the company, the visa was invalidated or maybe withdrawn by the ex employer, but he was never called to the embassy to do anything. I believe he mistakenly used the term 'revoked'. I am not sure if the contract had ended by that time, or if he quit before finishing it, which would then, I guess, create an issue for him if he wanted to apply for a work visa again.