(CNN) — Millions of Americans expecting to fly this month could have their plans grounded if the government shutdown drags on.

Starting Friday, the Trump administration will reduce flights at 40 airports nationwide if the shutdown continues.

The Federal Aviation Administration’s “Core 30” airports are among those on a preliminary list of sites expected to be impacted, an FAA source with direct knowledge of the situation told CNN.

Here’s what to know if the travel nightmare turns into reality Friday:

Which 40 airports will lose flights?

The “Core 30” high-traffic airports include New York City’s three major hubs and large airports in Atlanta, Boston, Chicago, Dallas, Denver, Honolulu, Los Angeles, Las Vegas, Miami, Phoenix, Seattle and Washington, DC, the source said.

Another 10

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