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Washington CNN  — 

The Department of Homeland Security has had to cancel some Global Entry appointments as the summer travel season heats up as it transfers people to help at the southern border, a department official tells CNN.

Global Entry is a Customs and Border Protection program that “allows expedited clearance for pre-approved, low-risk travelers upon arrival” in the US. The Trusted Traveler Programs website, which includes Global Entry, already has an alert warning applicants that the “extended partial government shutdown has resulted in a backlog,” of applications and renewals.

The personnel shift comes amid a swell of migrant families and children that have arrived at the US border this year. The influx has strained DHS immigration resources and caused concerns about overcrowding and delayed US Border Patrol processing.

In response to efforts at the border, “CBP is temporarily reducing staff at Global Entry Enrollment Centers nationwide and reassigning them to support frontline traveler processing during the busy summer months,” Customs and Border Protection said in a statement.

“Regrettably, this situation has forced the cancellation of some scheduled appointments and may make it difficult to schedule an immediate interview,” the statement said.

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The Trump administration has been pressuring Congress to pass emergency supplemental funding to assist agencies that are dedicating resources to the border and related needs. Last month, the White House requested $4.5 billion in emergency funding, including $3.3 billion for humanitarian assistance, $1.1 billion for border operations, and $178 million for mission support, like additional personnel.

The DHS official said that without the supplemental funding, the department might have to release adults from custody, or make cuts to other programs, which could increase airport travel and other wait times.

In order to help with enrollment, CBP suggests that travelers reschedule their appointment for a later date with the expectation that availability for appointments will be limited through September 30, 2019.

Additionally, CBP points out that conditionally approved Global Entry applicants can complete their interview without advance appointments at participating airports when arriving at the US on an international flight.