The U.S. Department of Transportation has announced that American Eagle Airlines became the first airline to be slapped with fines for violating the Department’s three-hour limit for tarmac delays.

On May 29, 2011, 15 different American Eagle Airlines flights left 608 passengers sitting on the Chicago O’Hare International Airport tarmac for a total of 225 minutes — 45 minutes beyond the limit.

For the violation, American Eagle Airlines has received a fine of $900,000 — the largest fine to date in a consumer case not involving civil rights violation. $650,000 must be paid within 30 days, and up to $250,000 can be credited for refunds, vouchers, and frequent flyer mile awards provided to the May 29th passengers, as well as to passengers on future flights that experience lengthy tarmac delays.

The rule, which was put in place in April 2010, states that any U.S. airlines operating with 30 or more passenger seats are prohibited from allowing their flights to remain on the tarmac for more than three hours without giving passengers an opportunity to deplane.

“We put the tarmac rule in place to protect passengers, and we take any violation very seriously,” explained U.S. Transportation Secretary Ray LaHood. “We will work to ensure that airlines and airports coordinate their resources and plans to avoid keeping passengers delayed on the tarmac.”

And it seems to be working. In today’s press release, the Department notes that between May 2010 and April 2011, the larger U.S. airlines required to file tarmac delays reported 20 tarmac delays of more than three hours but less than four hours. By comparison, during the 12 months before the rule took effect, these carriers had 693 tarmac delays of more than three hours, and 105 delays longer than four hours.

But tarmac delays persist, and JetBlue may be the next airline to incur heavy fines from the Department. On October 29, 2011 a JetBlue Airways Airbus A320 left passengers stranded on the tarmac for over 7 hours at a Connecticut airport after the plane was diverted when severe weather struck the northeast. More than 100 passengers on that JetBlue flight were left onboard without food, water or functioning bathrooms. If the government determines that the airline violated the tarmac delay rule, JetBlue could be fined as much as $27,500 per passenger.

Next week, airlines and airports alike will be on high alert to avoid delays as 23.2 million passengers take to the air for Thanksgiving weekend. As ABC News’ Matt Hosford noted, the Air Transport Association’s Thanksgiving travel forecast predicts there will be 37,000 fewer passengers per day compared to last year. But don’t expect empty seats — flights will still be full despite the 2 percent drop as U.S. carriers have reduced capacity to match demand. If you are flying for Thanksgiving, the ATA says the busiest days will be Friday, Nov. 18, Sunday, Nov. 27, and Monday, Nov. 28.