Airlines have increasingly relied on code sharing to branch out to new markets without investing in extra planes and staff. But the U.S. Department of Transportation now wants airlines to identify the actual carriers for an entire route before tickets are purchased.

Anyone who has flown for business or leisure in the United States — or overseas — in the last few years probably has experienced what the airline industry calls code sharing.

It happens when an airline sells you a ticket but books a portion of your journey on a small regional operator or another large airline, often without telling passengers or with easy-to-overlook notification. That can leave passengers confused or flying on an airline that they’d rather avoid, such as a small carrier.

Airlines have increasingly relied on code sharing to branch out to new markets without investing in extra planes and staff.

But the U.S. Department of Transportation (DOT) now wants airlines to identify the actual carriers for an entire route before tickets are purchased.

The DOT announced recently that airlines and travel websites have 60 days to modify their websites to clearly identify the airlines that will serve the passengers under code-sharing agreements.

“When passengers buy an airline ticket, they have the right to know which airline will be operating their flight,” Transportation Secretary Ray LaHood said.

The DOT order clarifies provisions of a law adopted last summer after a regional jet crashed in 2009 near Buffalo, killing all 49 aboard and one person on the ground. The turboprop plane was operated by Colgan Air, a regional carrier working with Continental Airlines. Investigators largely blamed crew error for the crash.

Although airline officials insist that pilot training and working conditions are the same for large airlines and regional carriers, backers of the law say passengers should know before buying a ticket on which airline they would be flying.

In December, the DOT fined JetBlue Airways $600,000 for violating disability access rules and failing to disclose a code-sharing agreement with a regional carrier, Cape Air. DOT investigators discovered the violation by calling JetBlue reservation agents and posing as potential passengers.