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CHICAGO (NewsNation Now) — Winter storms, equipment problems and other unforeseen issues can leave passengers stuck on a plane for hours, not able to get off, but also not going anywhere.

According to the U.S. Department of Transportation (DOT), U.S. airlines must follow tarmac delay rules.

After two hours, passengers are entitled to a snack and water during a tarmac delay, which occurs when an airplane on the ground is either awaiting takeoff or has just landed and passengers do not have the opportunity to get off the plane.

Airlines are also required to provide working toilets, comfortable cabin temperatures and adequate medical attention, if needed, according to the DOT.

Violation of these regulations can cost airlines huge fines.

In September 2021, United Airlines faced $1.9 million in fines, the largest fine assessed by the DOT for tarmac delay violations, for 25 different flights that violated the tarmac rules.

For all flights landing at or departing from U.S. airports, airlines can not keep passengers on planes longer than three hours for a domestic flight and four hours for international, unless there’s a specific safety issue.

The increase in flight delays and cancellations when bad weather appears is partially due to these tarmac laws. Airlines would rather preemptively cancel flights than face millions in fines after leaving passengers stranded on the tarmac during a snowstorm.