It is generally understood that employers have the right to read employees' emails sent and received through the corporate email system. The system is owned and operated by the employer, and employees should have no expectation that such communications are private.
What about electronic communications that are not stored on an employer's server - for example, text messages from mobile devices? Can an employer legitimately intercept those communications without the employee's consent? According to the 9th Circuit in Quon v. Arch Wireless, the answer might be no. For those who want more information, Workplace Privacy Counsel has the details.
The bottom line for companies is that Internet Service Providers, text messages services, and online email services (such as Yahoo or Gmail) are prohibited from disclosing stored messages without the consent of the sender or the recipient. This ruling, however, should not affect an employer's ability to control its own property, such as cell phones or computers that it owns and provides to employees to use. The key is for companies to have clearly written electronic communications policies that spell out the expectations, and make it clear to employees that they have no expectation of privacy in the use of any corporate-issued equipment.