Nearly 500 airport security officers have quit since the start of a partial government shutdown in February as long lines continued to snarl airport traffic around the country, the Homeland Security Department said Thursday.

The dispute that has forced 50,000 Transportation Security Administration officers to work without pay since mid-February is leading to major strains and the longest lines in the ​agency’s history — topping four hours in some locations.

TSA reiterated on Wednesday that the agency could be forced to close smaller airports if staffing ​issues worsened. More than 11% of TSA officers, or 3,120 officers, did not show up for work Wednesday.

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(Reporting by David Shepardson; Editing by Chizu Nomiyama)