First since the original comment was about government employees it is important to point out that Snowden was a contractor and not a government employee.

Although no form of protection from employment retaliation was in place at the time of Snowden's information release the Intelligence Community Whistleblower Protection Act of 1998 did provide a process for intelligence community employees and contractors to raise issues. Snowden didn't follow the procedures of the act and his direct release of classified material is not protected by the act nor would any laws passed since to strengthen whistleblower protection provide any defense for such a release of classified material.

Intelligence Community Whistleblower Protection Act of 1998 requires a whistleblower to raise any issues to the Department of Justice for review. The DoJ evaluates any issues raised and if they determine they may be credible will report the issues and supporting material to the Senate and House Intelligence committees along with starting their own investigation. If the DoJ determines they issues are not credible the employee and contractor can present the issue and any supporting classified documentation to the Senate and House Intelligence committees themselves.