A federal appeals court has made it more difficult for employers to legally snoop on their workers' e-mails and text messages sent on company accounts.

Under a Wednesday ruling by the 9th U.S. Circuit Court of Appeals, employers that contract an outside business to transmit text messages can't read them unless the worker agrees.

Users of text messaging services "have a reasonable expectation of privacy" in their messages stored on the service provider's network, Judge Kim Wardlaw wrote in the three-judge panel's unanimous opinion.

The ruling also lets employers access employee e-mails only if they are kept on an internal server.

The text message part of the ruling will affect more employers. According to analysts, the majority of U.S. companies pay outside parties to transmit their workers' text messages but most keep their workers' e-mail on internal servers.