Four senators wrote President Obama criticizing a recent signing statement for “discouraging” federal workers from blowing the whistle on “improper behavior,” adding that he should enforce whistle-blower protections in accordance with the law.

The members were reacting to a signing statement from Obama that he issued alongside the National Defense Authorization Act, in which he promised to “supervise, control, and correct employees’ communications with the Congress” if they broke the law in leaking information.

“Your statement could be perceived as potentially eroding protections for federal workers and discouraging employees from reporting improper conduct,” the bipartisan, bicameral group of lawmakers wrote in a letter first reported by The Huffington Post.  “The Legislative Branch has the Constitutionally-mandated authority and responsibility to oversee the Executive Brach, and federal employees and government contractors have the right and obligation to bring information to Congress in a lawful manner.”

The text of the NDAA extended whistle-blower protections to non-defense federal contractors, although it created an exception for employees working in intelligence.

Obama’s Justice Department has indicted six people under the Espionage Act for allegedly leaking nation security information, more than all the presidents combined since the law was signed during World War I.