The recalls come as federal agencies cope with the 25-day-long impasse by expanding the types of duties they consider essential, including tasks that have fueled public relations nightmares for agencies in charge of health and safety.

Details on some recalls were hard to come by Tuesday — because agencies had furloughed most of their spokespeople. But these are among the agencies adding to their rosters of on-duty workers even as the shutdown shows no signs of ending:

Federal Aviation Administration

More than 3,600 additional FAA employees are back at work compared with when the shutdown started in December, according to an updated Department of Transportation document published Tuesday. The move comes after union leaders complained that furloughs of inspectors had left the airlines “self-regulating,” a trend they said would eventually compromise public safety.

“We are recalling inspectors and engineers to perform duties to ensure continuous operational safety of the entire national airspace,” an FAA spokesperson said Tuesday. “We proactively conduct risk assessment, and we have determined that after three weeks it is appropriate to recall inspectors and engineers.”

Michael Gonzales, a vice president with the Professional Aviation Safety Specialists union, said around 1,500 inspectors have been brought back to work effective Tuesday.

DOT has also recalled more than 100 workers at the U.S. Maritime Administration and made slight adjustments to the counts of furloughed employees at other subagencies, according to the updated document.

Internal Revenue Service

The IRS said Tuesday that it expects to have 46,052 employees on the job — more than half its workforce — if the shutdown stretches into the start of tax-filing season in late January. That would be a huge jump from its initial shutdown plan, which kept only 9,946 workers on the job.

The IRS’s revised shutdown plan said it will continue to process taxpayer refunds because that money is drawn from a “permanent, indefinite refund appropriation” it can tap despite the shutdown. The White House budget office announced last week that the IRS would issue tax refunds despite the shutdown, in a reversal of previous policy.

But many other functions will be shuttered or curtailed, the IRS warned. It will not conduct audits, and collection activities will be generally limited to those that are automated. The agency said it will have some people who can answer phone calls with questions, though the public should be prepared for longer wait times.

People who send snail mail to the agency should expect lengthy delays, the IRS said. The agency’s walk-in “taxpayer assistance centers” will be closed.

“While the government is closed, people with appointments related to examinations (audits), collection, appeals or taxpayer advocate cases should assume their meetings are cancelled,” the agency said.

Food and Drug Administration

The FDA, which has furloughed about 40 percent of its staff, said Tuesday that it’s bringing 400 more people back to work. The “vast majority are inspectors and others are to support inspectors,” agency Commissioner Scott Gottlieb said on Twitter, which was serving as a quasi-official medium for many of the agency’s shutdown announcements.

“About 150 of 400 are focused on food inspections, rest are focused on other aspects of mission including medical devices (about 100 staff), drugs (about 70 staff) and biologics (90 staff),” Gottlieb added.

Under the agency’s initial shutdown plan, most routine food safety inspections were halted, while unpaid workers were still carrying out tasks such as active investigations of foodborne illness outbreaks.

Gottlieb had said last week that FDA planned to restart food safety inspections at facilities that handle riskier products like fresh-cut produce and seafood. Even when fully funded, however, FDA is not inspecting such facilities very frequently.

Interior Department

Interior’s new plan said it would designate dozens of employees as exempted from the furlough if the lapse in appropriations continued past Tuesday. The recalled employees include those working on offshore oil and gas lease sales, including one planned for March.

“Failure to hold these sales would have a negative impact to the Treasury and negatively impact investment in the U.S. Offshore Gulf of Mexico,” the bureau said. Its original contingency plan released in December did not include recalls of furloughed employees to help prepare the lease sale documents.

Interior has already said its Bureau of Land Management would continue processing onshore drilling applications during the shutdown.

The department’s plans to continue with onshore oil permitting had already drawn fire from Democrats who said the administration is overly focused on drilling over other types of government services, such as health care for American Indian tribes.

“Of all the things that have hit the public lands, of all the things that have hit Indian country because of the shutdown, that whole permitting process continues,” House Natural Resources Chairman Raúl Grijalva (D-Ariz.) told POLITICO.

Environmental Protection Agency

An updated version of EPA’s shutdown plan shows it now considers 28 employees “necessary to the discharge of the President’s constitutional duties and powers,” up from 12 in the plan’s December iteration. The agency also increased the number of people considered “necessary to perform activities necessarily implied by law” from zero to 12.

EPA also increased the number of workers “necessary to protect life and property” from 794 to 845. That category includes employees such as security guards, emergency response personnel and scientists keeping crucial experiments running.

The total number of EPA workers still on the job, including 53 embedded Public Health Service officers, is now 944, or 6.8 percent of its total workforce.

The agency previously said it had “excepted a limited number of employees” who are authorized to help Wheeler prepare for his confirmation hearing, which the Senate is holding Wednesday despite being unable to find a way to reopen the government. Democrats on the Senate Environment and Public Works Committee cried foul last week about that use of agency resources.

“It is difficult to understand how preparing you for next week’s confirmation hearing credibly falls within any of the categories listed in EPA’s Contingency plan, particularly the category of employee that is ‘necessary to protect life and property,’” Sens. Tom Carper of Delaware, Sheldon Whitehouse of Rhode Island and Ben Cardin and Chris Van Hollen of Maryland wrote in a letter to Wheeler.

The agency defended its actions.

“Participation in and preparation for a confirmation hearing that has been scheduled by Congress is clearly excepted under Department of Justice, Office of Legal Counsel, opinions,” EPA General Counsel Matt Leopold said in a statement last week. “Additionally, the Constitutional appointment power allows for EPA to take the steps necessary to ensure the Acting Administrator is prepared for his hearing.”

Bernie Becker, Eric Wolff, Katy O’Donnell, Helen Bottemiller Evich and Sarah Karlin-Smith contributed to this report.