NEW YORK (AP) — Armed federal immigration officers in tactical gear moved through terminals at some of the busiest U.S. airports Monday, standing near security lines and checkpoints after President Donald Trump ordered their deployment during a partial government shutdown that has disrupted air travel nationwide.

The officers were not making arrests or screening passengers. The Trump administration vaguely said they would supplement Transportation Security Administration staffing at certain airports. But after a year of intensified immigration enforcement and protests in cities across the country, their appearance at airport checkpoints has unsettled some travelers and raised new questions about how far their presence might extend.

On Monday, Associated Press journalists observed Immigration and Customs Enforcement officers and agents patrolling terminals and lingering near long lines of passengers at Hartsfield–Jackson Atlanta International Airport, John F. Kennedy International Airport in New York, Newark Liberty International Airport in New Jersey, George Bush Intercontinental Airport in Houston and Louis Armstrong International Airport outside New Orleans. A handful of other airports — including Phoenix's Sky Harbor International and William P. Hobby Airport in Houston — also confirmed ICE would be on site.

Federal law enforcement officers are a routine presence at international airports. Customs and Border Protection officers screen arriving passengers, and Homeland Security Investigations agents conduct complex criminal inquiries tied to cross-border activity. But immigration agents are rarely visible at TSA checkpoints, the front line of domestic air travel — and their presence there, even in a limited role, stands out.

ICE deployments arrive amid ongoing Washington impasse

Monday’s deployments came as hundreds of thousands of Homeland Security workers, including from the TSA, have worked without pay since Congress failed to renew DHS funding last month.

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. But the stalemate only deepened with Trump rejecting the latest offer, this one from his own Republican party, after a weekend of negotiations.

The White House staff pitched Trump on the idea of funding DHS, except for the immigration operations that have been central to the dispute, according to a person a familiar with the situation and granted anonymity to discuss the private talks. Still, Trump rejected that plan and later Sunday escalated his demands that senators also approve the so called SAVE America Act, a strict proof-of-citizenship voting bill that has essentially no chance in the Congress.

The White House on Monday turned down a request from top Democratic negotiator, Sen. Patty Murray of Washington, to meet that morning and continue talks, according to another person granted anonymity to discuss the private conversations.

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.

Unlike many recent immigration operations in U.S. cities, where federal agents have often worn face coverings, ICE officers at airports Monday appeared to be largely not masked — following an earlier direction by Trump.

Fears that the deployments will heighten tension

Some fear that positioning federal immigration officers at security checkpoints will only escalate tensions. Union leaders representing aviation workers stressed that ICE officers don’t have the same training and expertise as TSA workers — and the presence of federal immigration officers could also put some travelers on edge.

Everett Kelley, national president of the American Federation of Government Employees — which represents TSA officers — said in a statement that his members “deserve to be paid, not replaced by untrained, armed agents who have shown how dangerous they can be.”

Whether ICE will have a more sweeping role beyond watching long lines and patrolling terminals has yet to be seen. On Sunday, Trump said federal immigration officers could assist TSA by guarding exit lanes or checking passenger IDs — and the president has since suggested he could deploy the National Guard at airports, too.

ICE and TSA have been “working together so far very well," Trump said at a Monday public safety roundtable in Memphis. Still, he said he would “bring out the National Guard” if more personnel is needed.

Long wait times persisted at some major hubs Monday.

Atlanta’s Hartsfield–Jackson, for example, is still urging passengers to allow at least four hours for both domestic and international screenings. The check-in line for departing passengers was so long Monday that it snaked from the TSA screening area to the atrium, through the baggage claim and out the entrance doors with people in back of the line waiting outside. But ICE agents were not seen checking IDs or otherwise interacting with passengers.

“I may miss my flight that’s in one hour,” said Jeffrey Lewis, who was waiting in line Monday hoping to catch his flight from Atlanta to Phoenix. “I think that the government is full of it. I really do.”

Beyond TSA operations, many travelers on the East Coast faced additional disruptions after a Sunday night collision that killed two people and injured dozens of others on the runway of New York’s LaGuardia Airport. LaGuardia was temporarily shut down as air traffic was diverted for much of Monday.

TSA workers have been going without pay

After weeks of missed paychecks, many TSA agents have called 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.

TSA callout rates climbed over the weekend. Nationwide on Sunday, 11.8% of TSA agents missed work — the highest rate of the shutdown so far — with more than 3,450 officers calling out, according to DHS. More than 400 officers have quit during the shutdown, the department said.

Some have accused the government of using TSA workers as pawns in the ongoing budget fight. And aviation unions have raised additional safety concerns in light of the Trump administration’s deployment of federal immigration officers.

“This latest threat of ICE invasion at the airports is another distraction from solutions that protect Americans,” a coalition of unions representing aviation 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 — noting that, in contrast, ICE officers are among DHS workers who have continued to see paychecks as the partial shutdown drags on.

While routine funding that is used to pay TSA agents has lapsed, ICE and other immigration enforcement operations are funded with personnel receiving paychecks thanks to Trump’s big tax cuts bill that became law last year. It ballooned the DHS budget for immigration detention and deportation by billions.

Major Airport Call Out Rates from 3/22 (New Orleans reporting the highest number of call outs):

BWI 38.1%

JFK 37.4%

PIT 24.7%

PHL 24.2%

LGA 21.7%

IAH 39.1%

PHX 20.3%

MSY 42.3%

ATL 41.5%