(CNN) -- The federal shutdown is about to hit those who keep an eye on the nation's 100 commercial nuclear power plants.
The Nuclear Regulatory Commission said Monday it expects to furlough some 3,600 employees at the close of business on Thursday if Republicans and Democrats in Congress still have not resolved their impasse over federal spending.
The 300 essential personnel who would stay on include about 150 so-called "resident inspectors." They serve as the NRC's eyes and ears at nuclear plants. They also include employees who support emergency response, investigators, a skeleton management team, the five NRC commissioners and a few commission staff members, the NRC said.
The retained group would also include employees who support emergency response, investigators, a skeleton management team, the five NRC commissioners and a few commission staff members, the NRC said.
There are 100 commercial nuclear reactors at 63 sites nationwide.
"We are going to make sure that we continue our oversight of the plants because the resident inspectors will be on duty, and we are prepared to respond to an emergency on short notice," NRC spokesman Eliot Brenner said when asked how furloughs might impact safety.
In a blog post, Mark Satorius, the agency's executive director for operations, said it has generally operated normally using "carryover" funds, but that it cannot continue beyond midweek without new funding from Congress.
In the event of a nuclear-related emergency, he said, additional NRC employees can be recalled.
"We sincerely regret these actions are necessary and are eager to resume our important mission as soon as possible," he said.
Nuclear industry watchdogs said the furloughs were cause for concern.
"Yes, I am worried," said Ed Lyman, senior scientist with the Union of Concerned Scientists. "It's not good for anyone and it's certainly not good for the agency that needs to safeguard our nuclear power plants against accidents and terrorism, and it's certainly not good for the American people. If there's an emergency of course, they'll call back more people. But it's just counterproductive to go through the motions of furloughing a lot of people."
Lyman said furloughs will stall changes the NRC is making in response to the Fukushima disaster in Japan. "But the most acute issue is assuring that the operating reactors" are safe.
"I'm not expecting overnight that it's going to be a collapse of safety," he said. "You can only hope for the best that a situation doesn't occur during this time."