ATLANTA (AP) — More federal immigration officers are making their way to U.S. airports after President Donald Trump said he’d deploy them to supplement the Transportation Security Administration during a government shutdown that has caused long lines at security checkpoints across the country.

On Monday morning, a handful of federal officers were seen by The Associated Press near busy lines at Hartsfield–Jackson Atlanta International Airport. And a handful of other airports — including Louis Armstrong International in New Orleans, as well as Houston’s George Bush Intercontinental and William P. Hobby airports — said Immigration and Customs Enforcement officers would also be on site to support TSA operations.

Federal officers are a routine presence at international airports, where Customs and Border Protection officers screen arriving travelers and Homeland Security Investigations agents handle criminal cases tied to smuggling, trafficking and fraud. But what’s unusual in the current moment is their visibility at TSA security checkpoints.

Monday’s deployments came as hundreds of thousands of Homeland Security workers, including from the TSA, U.S. Secret Service and Coast Guard, have worked without pay since Congress failed to renew DHS funding last month. That’s led many TSA agents to call in sick — or even quit their jobs — as financial strains pile up. The staffing shortages have forced some airports to close checkpoints at times, with wait times swinging dramatically for travelers.

On Sunday, the Trump administration signaled it would deploy federal immigration officers to large airports with the longest wait times — and Department of Homeland Security spokesperson Lauren Bis said that would include “hundreds” of ICE officers, but she did not disclose all the airports they would go to, citing security reasons.

Some fear the move to deploy federal immigration agents will only escalate tensions.

“This latest threat of ICE invasion at the airports is another distraction from solutions that protect Americans,” a coalition of unions representing flight attendants and other workers — including the Association of Flight Attendants-CWA and International Association of Machinists and Aerospace Workers — said in a Sunday statement. Transportation security officers “can’t simply be replaced” by federal immigration officers, they noted, adding that ICE’s presence and potential attempts to question passengers about immigration status may also “distract them from ensuring airport security.”

The unions called for TSA workers to be paid immediately.

Trump said on Sunday that he would order federal immigration agents to airports to assist TSA by guarding exit lanes or checking passenger IDs unless Democrats agreed to fund the DHS. Funding for the department lapsed Feb. 14, as Democrats refused to fund ICE as well as Customs and Border Protection without changes to their operations in the wake of the deaths of Alex Pretti and Renee Good in Minneapolis.

Democrats are continuing to demand major changes to federal immigration operations — including policy changes that would require ICE officers to get a warrant from a judge before forcefully entering homes, the removal of masks and clear identifying information on uniforms.

Trump on Monday directed ICE officers not to wear face coverings in their work at airports. In a social media posted, Trump said he supports ICE officers wearing masks when dealing with “hardened criminals” but suggested it isn’t necessary “when helping our Country out of the Democrat caused MESS at the airports.”

Beyond TSA operations, New York’s LaGuardia Airport shut down following a deadly collision on the runway late Sunday. An Air Canada regional jet struck a fire truck while landing, officials said — killing the pilot and copilot while around 40 passengers and crew members were taken to area hospitals, some with serious injuries.

According to the FAA, LaGuardia is expected to remain closed until at least 2 p.m. ET on Monday. Air traffic has been diverted, and Monday morning operations also were halted at Newark Liberty International Airport in neighboring New Jersey.

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Grantham-Philips reported from New York. Associated Press writer Collin Binkley in Washington contributed to this report.

Emilie Megnien And Wyatte Grantham-philips, The Associated Press