@yry/dht- Not entirely correct.
The laws vary by state but, in general, a potential employer can confirm your final salary with a previous employer. Using the number you provide, they can ask "we have their salary as $___. Is that correct?" Your previous employer can (usually) answer that question.
I believe Massachusetts just passed a law to say that previous salary info cannot be requested or disclosed as part of an employment application. In all other states, there is some way to get the info.
Also note that, for defense contractors in particular, it is common to have to supply a last pays tub from previous employer as part of the hiring process. DO NOT LIE ON APPLICATIONS. It can result in having your job offer rescinded.