Federal agents aren't getting paid during shutdown, but also have to pay for expenses

While many families were enjoying Christmas, an undercover FBI agent was communicating with a man who was suspected of plotting an attack on the White House, court documents show.

It was days after the government initially shut down and the agent was not getting paid. But the work resulted in the arrest of Hasher Jallal Taheb, a man in Georgia who federal authorities accused of plotting to attack several prominent locations in Washington, including the White House.

And now as the partial government shutdown is in its fourth week, federal employees are furloughed or not receiving pay for the work they are doing.

But agents and investigators from the FBI, Homeland Security and Secret Service are concerned they won't be reimbursed in a timely fashion for business expenses.

Don Mihalek, the Secret Service representative to the Federal Law Enforcement Officers Association confirmed to ABC News that cash advances are not being given out and official credit cards are not being paid for through government invoice channels.

"The way that works is FBI agents have an FBI credit card but they have to pay the bill," FBI Agents Association spokesperson Paul Nathanson told ABC News. "These agents have to buy tickets to go overseas and they can't get reimbursed for that money. So not only are they not getting paid, they're putting out money for their jobs and not getting it back until the government opens."

John Cohen, a former acting undersecretary for Intelligence and Analysis at the Department of Homeland Security and an ABC News contributor, said the cost burden has caused low morale for agents.

"In conversations I'm having with law enforcement officials, the shutdown has reached the point where it could impact public safety," Cohen said.