United has hit a few speedbumps as it has consolidated its flight operations with Continental, with March proving to be a particularly bad month for the nation’s second largest carrier.

“United Airlines racked up the highest number of consumer complaints of any U.S. airline — and ranked among the bottom in on-time performance — in March, the month it switched to Continental Airlines’ reservation system, as well as a single frequent-flier program and website,” wrote the Houston Chronicle‘s Kiah Collier.

Some 260 complaints about United Airlines were reported to the U.S. Department of Transportation in March, representing 34 percent of all complaints that month, according to the latest Air Travel Consumer Report (PDF), put out each month by the U.S. Department of Transporation’s Office of Aviation Enforcement and Proceedings. The bulk of those complaints were about flight problems, issues with the reservation and ticketing system, and customer service.

Things weren’t going well for the carrier in the previous month either: in February, United was the subject of 132 complaints, or 24 percent of the monthly total.

Only 77.43 percent of United flights arrived on-time in March, putting it in the bottom three U.S. carriers for that metric.

In an email to Collier, United spokesman Rahsaan Johnson admitted that March “was a tough month” for the carrier, but efforts are underway to continue “improvement in on-time performance and customer service.”