The 1912 Lloyd–La Follette Act

The Lloyd–La Follette Act of 1912 began the process of protecting civil servants in the United States from unwarranted or abusive removal by codifying "just cause" standards previously embodied in presidential orders. It defines "just causes" as those that would promote the "efficiency of the service." August 24, 1912, § 6, 37 Stat. 555, 5 U.S.C. § 7511

The Act further states that "the right of employees… to furnish information to either House of Congress, or to a committee or Member thereof, may not be interfered with or denied." 5 U.S.C. § 7211

https://en.wikipedia.org/wiki/Lloyd%E2%80%93La_Follette_Act