He said the shutdown would contribute to a backlog of about 5,000 disability appeals cases in Baltimore.
Randy Frye, president of the administrative judges' association, said the group's position is that the staff as well as the judges should be considered essential.
In Monlyn's case, the decision to furlough most members of his National Association of Government Employees union local came as a surprise. As recently as Friday, he said, they had been assured by managers that they would remain on the job. But when they reported Tuesday, he said, all but seven of the 120 to 125 members were sent home.
Monlyn, who is president of NAGE Local R-386, said he and other union members are "dual status" employees — holding National Guard jobs as both civilians and military members. Among the work they perform is maintaining humvees, tanks and helicopters, gate security at National Guard posts, and secretarial services.
In the event of a natural disaster or civil disruption, he said, their absence could impede the Guard's readiness.
"It's quite disturbing," he said.
Monlyn, 37, who is a sergeant in the D.C. National Guard, said the furlough comes just as they were beginning to recover from the economic effects of seven furlough days during the summer.
Government workers have not actually been labeled "essential" or "nonessential." Officials prefer to say "excepted" or "nonexcepted."
One reason is concern that the term "nonessential" would affect the morale of employees given that label. It also could create an opening for small-government conservatives to question whether those jobs should exist at all.
"The very fact that government agencies and organizations have nonessential personnel present in the first place could be viewed as testament to our bloated, overfunded ... unsustainable government," commentator Jeff Emanuel wrote in a 2011 article on RedState.com.
Many of the functions of furloughed workers are widely viewed as critical even if they can be deferred for a limited time. Examples included compilation of government employment statistics, auditing banks covered by federal insurance and maintaining National Guard equipment.
Monlyn said that when managers gathered workers to notify them of the furloughs, they reassured them that "everybody's essential."
He was not appeased.