PHILADELPHIA — Sen. Bob Casey, D-Pa., has urged the chief executive officer of US Airways to rescind the airline’s fare increase planned for flights between Philadelphia and Pittsburgh in early January, when only US Airways will fly between the two cities.

When Southwest Airlines drops its flights between Philadelphia and Pittsburgh on Jan. 8, the price for a US Airways round-trip ticket will jump from $118 plus tax, to $698 plus tax.

A check of US Airways’ website Wednesday found the $118 fare ($140 with tax) was for passengers who stayed in Pittsburgh multiple nights. The $698 fare ($720 with taxes) was for nonstop flights within the same day: fly out in the morning and back at night.

For travelers who stay one night, the fare dropped to $531 with taxes and fees, and was even lower for passengers who stayed multiple nights, or on a Saturday night.

Airfares can fluctuate several times a day, and vary widely depending on the time, day and how full planes are.

The highest fares for nonstop and same-day travel are aimed at business travelers. Those fares are traditionally higher than for leisure passengers who can stay multiple nights.