WASHINGTON, D.C. — The Department of Transportation today issued new guidelines restricting how long airlines can hold passengers on the tarmac during delays.

The regulations were prompted after an August incident in which a flight was diverted to Rochester, Minn., and then held on the tarmac all night. Passengers were given only one small snack and a drink, and the plane’s on-board toilets weren’t working properly.

Continental Airlines and ExpressJet Airlines (the flight operator) were fined $100,000 in the incident, while Mesaba Airlines, which provided ground operations for the flight, was fined $75,000.

Among the new rules:

• Airlines would be required to provide food and water after a two-hour delay.

• Passengers would have to be deplaned after three hours.

• And airline staff would have to keep the toilets working.

“Airline passengers have rights, and airlines have the obligation to respect those rights. Passengers want — and deserve — to be treated fairly, and these new rules will require airlines to do just that,” Transportation Secretary Ray LaHood said in a blog entry announcing the move.

Sen. Al Franken hailed the move.

“Their six-hour ordeal was unacceptable and unfortunately not an isolated incident,” Franken said. “I’m glad that with the new three-hour limit imposed by the Department of Transportation today, it won’t happen again.”

The new rule takes effect in 120 days.