The union that represents air traffic controllers sounded the alarm in a statement released Friday, expressing their concerns over air safety and working conditions amid the government shutdown. The comments came just hours after a ground stop was issued for New York's LaGuardia Airport due to staffing shortages.

"Air traffic controllers are required to report fit for duty every shift. It is a very high threshold of fitness demanded by the seriousness of the job," the statement said. "This shutdown has caused a tremendous amount of added stress for them on top of what is already a difficult and stressful job."

Unscheduled absences at two Federal Aviation Administration facilities forced air traffic controllers to halt certain flights into LaGuardia and slow departures from the airport on Friday morning. More than 800,000 federal employees, including air traffic controllers, missed their second paycheck due to the partial government shutdown on Friday.

Get Breaking News Delivered to Your Inbox

"What we're seeing is people having to make difficult decisions after getting no paycheck this week," Paul Rinaldi, the president of the National Air Traffic Controllers Association, said in an interview with CBS News Thursday. "We're starting to see real human consequences right now that people have to make real tough decisions and each individual has to make that decision. I cannot make that for them."

Financial hardship due to the government shutdown has prompted some federal airport workers to call out of work causing some passenger interruptions. On Friday morning, an American Airlines flight out of Monroe, Louisiana bound for Dallas with 26 passengers was cancelled due to a TSA officer shortage in Monroe, according to an airline's spokesperson. About 7.6 percent of the TSA workforce had an "unscheduled absence" Thursday, up from 3 percent a year ago, according to the federal agency.

Read the full statement from the National Air Traffic Controllers Association (NATCA):

"NATCA does not condone or endorse any federal employees participating in or endorsing a coordinated activity that negatively effects the capacity of the National Airspace System or other activities that undermine the professional image and reputation of the men and women we represent.

"Air traffic controllers take their responsibility to protect the safety of the flying public at all costs very seriously. Nothing else matters except safety.

"With that said, in the past few weeks, we have warned about what could happen as a result of the prolonged shutdown. Many controllers have reached the breaking point of exhaustion, stress, and worry caused by this shutdown. Each hour that goes by that the shutdown continues makes the situation worse.

"Air traffic controllers are required to report fit for duty every shift. It is a very high threshold of fitness demanded by the seriousness of the job. This shutdown has caused a tremendous amount of added stress for them on top of what is already a difficult and stressful job.

"We are at a 30-year low of fully certified air traffic controllers and as we have warned for several years, the efficiency of the system will be constrained when there is inadequate staffing to ensure the safety of all flights.

"The entire National Airspace System is extremely complex and interconnected, so when delays begin at one major facility, there is a ripple effect that reaches across the system. It affects all flights that are scheduled to use the airspace of facilities where staffing is inadequate to safely handle traffic volume."