An estimated 16.5 million travelers are expected to fly on U.S. airlines over the busy Labor Day travel period, according to an airline industry group.

Airlines for America says that's a 3.5 percent increase compared with travel volumes for the Labor Day period last year.

Friday is expected to be the busiest day, when an estimated 2.76 million passengers will be traveling on U.S. airlines, the group said.

It is expected to be busier than Thursday and Monday, with about 2.6 million people traveling each of those days.

The busy period for the holiday runs from the Wednesday before until the Tuesday after.

Saturday and Sunday will be less congested, and are among the lightest days of the year for air travel, according to Airlines for America.

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