Q. Is it possible for a prospective employer to verify your salary from a previous employer without your knowledge or consent?
A. It depends on whether your company belongs to a consortium of companies that exchanges information about their current and former employees. Typically, companies participating in such consortia may share pay data and the current status of their employees - for example, active or terminated.
Companies normally ask potential employees to sign a waiver allowing the employer to verify information provided on a resume or employment application. Declining to let a prospective employer verify your employment history could seriously jeopardize your candidacy.
It seems as if you don't want companies calling your previous employers to verify your salary. If that is the case, I would add a note to your resume and all employment applications that requires a company to inform you if and when they decide to contact a previous employer.
Rarely would a company contact a candidate's previous employer without permission.