Washington — Nearly 13,000 FBI agents will not get a paycheck Friday. The FBI Agents Association told the White House and Congress that without it, agents face "financial insecurity" and could lead some to find other work.

Ongoing FBI investigations have also been hampered by the partial government shutdown.

"As this moves forward, it's only going to get worse," said Thomas O'Connor, president of the FBI Agents Association. "People are nervous, they're upset and they're worried about when is the next paycheck going to come in."

There are similar concerns within other federal law enforcement agencies like the Drug Enforcement Agency and the Bureau of Alcohol, Tobacco, Firearms and Explosives. Sources tell CBS News morale is "horrible." Commanders are having to weigh financial constraints before approving certain sensitive undercover operations.

"You know the old adage, 'crime doesn't pay' ... and neither does the federal government. That's not right," O'Connor said.

Veteran agents have been through other shutdowns before, but sources said this time is different because the shutdown has dragged out longer. The FBI Agents Association speaks for its members and not the bureau — which isn't commenting Thursday.