In the email, Elam, the deputy federal security director overseeing Palm Springs, LAX and three other Los Angeles-area airports, acknowledged security staffing worries and warned of "disciplinary action" at Palm Springs airport.

"Management is appreciative and sensitive to the burden the ongoing government shutdown is placing on each one of you," Elam wrote. "You are an essential employee and you are required to report for work to carry out essential duties."

"Due to excessive unscheduled absences recently experienced at PSP (Palm Springs International airport) that has adversely impacted security operations, if you have an unscheduled absence, you will NOT be placed in an intermittent furlough status," Elam added. "Your unauthorized unscheduled absence will be coded by payroll as absent without leave (AWOL). At the conclusion of the government shutdown, an employee's AWOL status may result in progressive disciplinary action."