More than 8,000 U.S. flights were delayed on Sunday due to air traffic controller shortages amid a federal government shutdown now in its 26th day.

Airlines including Southwest, American, United, and Delta experienced significant delays, with some disruptions triggered by staffing shortages at major airports like O’Hare, Reagan National, and Newark Liberty.

About 13,000 air traffic controllers and 50,000 TSA officers are working without pay, leading some to seek second jobs and prompting concerns of increased delays as paychecks are missed, Reuters has reported.

The FAA warned that continued staffing shortages could worsen travel disruptions, while political disputes between Democrats and Republicans over funding and healthcare subsidies remain unresolved.