Delta Air Lines has been slapped with a $750,000 fine for bumping fliers against their will. During a recent investigation, the Department of Transportation (DOT) found that the airline failed to solicit enough volunteers to give up seats on overbooked flights and didn’t always offer cash compensation when required.

Delta said it is working to resolve the problem—and that it is settling part of the fine by loading up on tablets to give to airport agents to help them follow the rules on handling overbooked flights.

As I reported in "Fewer Flights and Higher Fares: Is This the Future of Air Travel?," airline overbooking continues to be a problem, especially in this era of packed planes—with load factors, or percentage of seats filled, having risen from 71 percent to more than 83 percent in the past decade. Even though most fliers are traveling on nonrefundable tickets, major airlines typically oversell flights (which is perfectly legal) to compensate for the small number of passengers who may fail to show up.

Because this is a problem that just won’t go away, the DOT has raised the compensation for passengers who are bumped, or, in DOT parlance, “involuntarily denied boarding,” and requires an airline offer cash on the spot to victims—not just a travel voucher. However, as our report reveals, not all airline employees appear to have gotten the memo, and don’t always inform travelers what they’re entitled to. So if you do get bumped, make sure you know your rights.