Air traffic controllers will miss their paychecks Tuesday because of the ongoing government shutdown, raising concerns that mounting financial stress could take a toll on the already understaffed employees who guide thousands of flights each day.

Flight delays are becoming more common across the country as more controllers call out sick because the Federal Aviation Administration was already so short on controllers before the shutdown.

Transportation Secretary Sean Duffy and the president of the National Air Traffic Controllers Association Nick Daniels have continued to emphasize the pressure that controllers are feeling. They say the problems are likely to only get worse the longer the shutdown continues.

The FAA restricts the number of flights landing and taking off at an airport anytime there is a shortage of controllers to ensure safety. Most of the time that has meant delays — sometimes hours long — at airports like New Jersey's Newark Liberty International Airport or Burbank airport in California. But over the weekend, Los Angeles International Airport actually had to stop all flights for nearly two hours.

Duffy said the shutdown is making it harder for the government to reduce the longstanding shortage of more than 3,000 controllers. He said that some students have dropped out of the air traffic controller academy in Oklahoma City, and younger controllers who are still training to do the job might abandon the career because they can't afford to go without pay.

AP video by Joseph Frederick