Welch said the bill will "prevent fishing expeditions into employees’ private lives."
"While an employer may have a valid concern about the business impact of an employee’s online activity, demanding passwords and unfettered access to private accounts is an over-the-top solution,” he said.
Outrage first erupted after The Associated Press reported last year that some bosses have demanded that job applicants provide passwords to their private Facebook accounts to check for embarrassing or damaging information.
The passwords give employers access to the users’ private messages, photos and the profiles of their friends.
The AP story cited mostly isolated incidents; it is unclear how widespread the practice is.
Eight states have enacted laws restricting the ability of employers to demand access to social media accounts, but federal legislation has so far made little progress.