The union representing Transportation Security Administration officers is urging the agency’s chief to allow its most vulnerable employees to stay home as cases of the novel coronavirus in the agency’s ranks climbs rapidly, topping 1,500 this week.

In the early stages of the pandemic, employees in high-risk health groups were allowed to stay home using weather and safety leave, and the agency’s regional directors reduced work schedules for everyone else, union leaders say. But in late June, just as the virus began taking hold again, the leave policy was canceled, and officers were ordered back to work, even though air passenger numbers were still down by about 70 percent.

Since then, virus cases among TSA employees have surged. On Friday, the union wrote to TSA Administrator David Pekoske asking for the previous leave policy to be restored.

“Your decision to implement WSL for high-risk employees correctly recognized that the Agency could continue to carry out its mission without having to sacrifice its most vulnerable employees, and this calculus has not changed,” wrote Hydrick Thomas, president of the AFGE Council 100. “Passenger throughput continues to be a fraction of what it was one year ago, the number of flights per day remains low, and the coronavirus continues to wreak havoc on vulnerable populations.”

The number of cases among agency employees has been growing rapidly in recent weeks, according to data assembled by The Washington Post using archived versions of the agency’s disclosure Web pages. While it’s not clear that officers are being exposed at work, the TSA has reported far higher rates of positive tests than either the Defense Department or Veterans Affairs Department, which also regularly disclose when employees have fallen ill.

Lisa Farbstein, a TSA spokeswoman, said the agency changed its policy in anticipation of needing more officers in advance of the July 4 holiday. Having extra officers available to work means passengers can be moved through checkpoints quickly while still being allowed to spread out, reducing their risk of being exposed to the virus.

“We want to keep the lines moving as efficiently as possible,” Farbstein said. She said wait times are at around nine minutes in normal checkpoint lanes and four minutes for TSA PreCheck passengers.

But Thomas, who knew the first TSA officer to die of covid-19 and lost a 27-year-old niece to the virus, said the agency has to do more.

“I don’t want to go to any funerals,” he said in an interview.

On March 15, the agency began reporting figures for employees who had tested positive, disclosing four at San Jose International Airport had fallen ill. In just six weeks, the TSA logged its first 500 cases.

Then, just as they did in the country at large, the number of new cases began to level off, not topping 1,000 until 10 weeks later on July 9. But since that date, the number of cases has been climbing more rapidly, taking just another four weeks to reach 1,500 on Tuesday.

Six agency employees have died of covid-19, the disease caused by the novel coronavirus, as has one contractor.

Nearly all the cases are among screening officers who check passengers’ baggage to make sure they’re not carrying anything dangerous through airport checkpoints. For much of the spring, high-risk officers were allowed to stay home without using their normal leave balances. Regional TSA leaders were able to reduce schedules for other employees.

But union leader Joe Shuker said almost every officer has been called back to work, only to find that they often have little work to do. Officers can do some training at computers and extra cleaning, he said, but end up standing around with little room to practice social distancing.

“We’re being exposed every day and for no reason,” said Shuker, who works at the Philadelphia airport.

Air travel has picked up again, with some 700,000 people passing through the agency’s checkpoints each day, but the numbers are still far below the typical 2.6 million or so for this time of year.

A TSA whistleblower came forward in June, alleging the agency had done too little to protect employees and the public from the virus and a federal watchdog ordered a formal investigation. In the meantime, the head of the agency met the whistleblower, and the TSA tightened its safety rules.

TSA officers are required to wear masks, and the agency has been installing plastic shields for them to work behind. On Wednesday, the TSA announced that it had awarded a $2.5 million contract to California-based Lavi Industries to install the shields at 37 “priority airports” and that the work would be completed by autumn. Officers are supposed to change their gloves after coming into contact with passengers and have to wear eye protection if they’re not behind a shield.

But in the letter to Pekoske, Thomas wrote the extra protective equipment did not do enough to resolve the union’s concerns about high-risk employees.

The TSA says employees can use other kinds of leave if they want to stay home. But the union questions what would happen when those balances run out.

“This pandemic is not permanent, but neither is it going away tomorrow,” Thomas wrote. “We believe that prematurely reverting to business-as-usual leave policies by requiring that high-risk employees who choose to prioritize their health and safety exhaust their own leave is myopic: it ignores the sheer scope of this once-in-a-lifetime crisis, it places an unfair burden on many on your front line, and it fails to provide a solution for the near future once the leave balances have been exhausted.”

On a visit to the Atlanta airport on July 22, Pekoske told workers they owed it to themselves and passengers to do everything they could to keep healthy.

“It’s really important that you practice social distancing, wear masks, wash your hands and avoid contact between your hands and face as much as you possibly can,” Pekoske said. “This is especially important going to and from your workplace and within your community. We need to do everything we can to prevent further spread.”

Other agencies that protect the air travel system have also suffered from the virus. The Federal Aviation Administration has reported positive or presumed positive cases at least 116 air traffic control facilities. Many of them have had employees test positive on multiple occasions, including one in Houston that has reported employees testing positive on 11 different dates since March 29.

The FAA has refused to release a total number of employees who have fallen ill. Officials don’t think cases are spreading at its facilities but reflect what is happening in the community.

“Employees in FAA facilities must wear face coverings when they are in common spaces or cannot socially distance,” the agency said in a statement. “We have a robust reporting process to ensure sick employees are not in the workplace putting others at risk, and a rigorous cleaning regimen when we learn that an infected employee has been in a facility.”

Disclosures by other federal agencies show the virus has hit the 60,000-strong TSA especially hard. The Defense Department, with some 750,000 civilian employees, has logged just 6,000 cases. The Department of Veterans Affairs, which employs about 380,000 people, has seen about 3,800 cases.

Customs and Border Protection has seen similar numbers of cases, reporting 1,766 among its workforce of 60,000.

For the purposes of claiming benefits under the Federal Employees’ Compensation Act, government workers in front-line jobs such as TSA officers and law enforcement agents are presumed to have been exposed to the virus at work. As of late last month, about 4,000 federal employees had filed for compensation.