The airline industry is facing a level of risk "we cannot even calculate" because of the partial government shutdown, unions representing air traffic controllers, flight attendants and pilots said in a statement Wednesday.

“We have a growing concern for the safety and security of our members, our airlines, and the traveling public due to the government shutdown," the presidents of the National Air Traffic Controllers Association, the Air Line Pilots Association, International, and the Association of Flight Attendants-CWA said. They added, "In our risk averse industry, we cannot even calculate the level of risk currently at play, nor predict the point at which the entire system will break. It is unprecedented."

The shutdown, already the longest in history, reached its 34th day on Thursday. About 800,000 federal workers are furloughed or working without pay. Of those, almost 50,000 are airport security workers who are considered "essential" and thus are working unpaid.

President Donald Trump has said he won't reopen the government unless he is given $5.7 billion in funding for a wall along the United States' southern border, which the Democrats have refused to do. They compare his tactics to holding the government hostage over his demands.

The union leaders said air traffic controllers, Transportation Security Administration officers, safety inspectors, air marshals, and federal law enforcement officials have been working without pay for more than a month. As the shutdown has dragged on, an increasing number of TSA workers have called out sick. About 7.5 percent of agents had "unscheduled absences" Wednesday — more than double the amount of workers who were out in the same time period last year.

"Staffing in our air traffic control facilities is already at a 30-year low and controllers are only able to maintain the system’s efficiency and capacity by working overtime, including 10-hour days and 6-day workweeks at many of our nation’s busiest facilities," the union leaders said. "Due to the shutdown, the [Federal Aviation Administration] has frozen hiring and shuttered its training academy, so there is no plan in effect to fill the FAA’s critical staffing need."

"The situation is changing at a rapid pace," they continued. "Major airports are already seeing security checkpoint closures, with many more potentially to follow. Safety inspectors and federal cybersecurity staff are not back on the job at pre-shutdown levels, and those not on furlough are working without pay."

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The union leaders said they "find it unconscionable" to ask their members to work without pay.

"To avoid disruption to our aviation system, we urge Congress and the White House to take all necessary steps to end this shutdown immediately," they wrote.

The FAA responded to the unions' concerns in a statement.

"The FAA continually reviews and analyzes the performance of the national airspace system to assess its safety and efficiency," an agency spokesperson said. "We have not observed any appreciable difference in performance over the last several weeks compared to the same periods during the previous two years. We remain grateful to the air traffic controllers for their professional (sic) and dedication to their safety mission."

The FAA said air travelers "can be assured that our nation's airspace system is safe."

But the strain on FAA employees was obvious in Oklahoma City, home of the agency's training center.

Allen Street had been slated to graduate from the months-long training program on Jan. 10, after moving to Oklahoma from Tennessee with his wife and their two-year-old daughter.

"We're out here without pay, waiting to to figure out the next step," he said. "I know people who have had to go back home. Some people like me are renting houses so there's no where else to go. Without pay it's difficult to go anywhere."

Ileta Young is an instructor at the academy who'd been doing volunteer work at the food bank. Now she's relying on the food bank to help her eat.

“I was on top of the world, working hard...being able to help my daughter when she needed it. And now I need help, now I need services, and that's the hardest thing, to have to stand in a soup line,” she said. "It's tough."

Small businesses that have federal contracts with the shuttered agencies have been hit hard by the shutdown as well.

A report Thursday by the U.S. Chamber of Commerce, a business lobbying group, estimated that 41,107 small business contractors have been impacted to the tune of $2.3 billion.

"During the government shutdown, affected agencies are not procuring goods and services from these small businesses. This not only impacts the cash-flow of small businesses during the shutdown, in some instances small businesses will be unable to make up the lost contract work or sales," the study says.

The analysis said businesses in every state have been affected. California has over 5,000 small businesses with government contracts, Virginia over 4,000 and Texas over 2,500.

"The pain being inflicted on American families and small businesses is significant," said Neil Bradley, the group's executive vice-president. "The pain is being felt throughout the United States."

The Chamber of Commerce sent a letter to the White House and Congress urging them to take immediate action. "The time to act, the time to end this shutdown is now so that we can keep the economy moving forward," the letter says.