The Federal Aviation Administration (FAA) has warned its employees regarding “restrictions on partisan political activity,” an internal FAA email obtained by TYT reveals.

“Employees are responsible for acquainting themselves with restrictions on partisan political activity and for not engaging in prohibited actions,” the email states. “It is important to ensure that remarks made in any forum regardless if made in connection with work or by a person identified as an FAA employee, comport with governing rules and regulations.”

The email was sent on January 9 by an FAA administrator, according to an FAA contractor who requested anonymity in order to avoid retribution. The subject line reads, “Internal Management Guidance Re: Expression of Views Reminder.”

At the time of this writing, the government shutdown is on its fourth week, representing the longest in U.S. history. President Trump has threatened to maintain the shutdown for “months or even years” if he does not obtain $5.6 billion for his southern border wall. He has also asserted that federal workers actually like the shutdown, despite its having left some 800,000 without pay.

In a separate email, another FAA administrator references the guidelines, saying, “Please be mindful of this guidance to avoid any unnecessary scrutiny.” This was a veiled threat to employees that they would be scrutinized for speaking out, TYT’s source said.

“These people are not allowed to speak out. They are expected to work without pay, though,” the source said.

In response to the previous FAA email, one disgruntled FAA employee replied sarcastically, “Isn’t there also guidance about getting paid to work and forcing folks to work without pay being illegal?” The response took the form of a reply-all email, also obtained by TYT, and went out to thousands of FAA employees, the source said.