Delta Air Lines had the highest rate of consumer complaints in May among U.S. airlines ranked in a federal report.

According to the U.S. Bureau of Transportation Statistics, Atlanta-based Delta's 2.14 complaints per 100,000 passengers boarding planes put it at the bottom of the ranking at No. 19 for the month. Most of the complaints against Delta were about baggage or flight problems, according to the report released Monday. The monthly report counts consumer complaints filed with the U.S. Department of Transportation.

Delta spokesman Kent Landers said Monday, "If you look overall at on-time performance, baggage handling, flight completion and most every metric, Delta employees are delivering great service."

He attributed the "unusual spike" in complaints to Delta's new $25 fee for a second checked bag. Delta did not waive the fee for passengers who booked flights before the airline posted information about the new fee on its Web site April 9. Last month, Delta said it would offer a rebate of the fee to customers who bought tickets from the airline before April 9 and traveled May 5 or later, "in response to customer feedback and as a matter of goodwill." The fee went into effect May 5.

"We did choose to respond to that feedback and make an exception," Landers said.

Orlando-based AirTran, which has its hub in Atlanta, ranked No. 16 in the consumer complaint ranking. Delta-owned regional carrier Comair ranked No. 10 and Atlantic Southeast Airlines, an Atlanta-based regional carrier for Delta, ranked No. 1 in May with the lowest rate of complaints.

In a ranking of airlines' on-time performance in May, AirTran came in at No. 3, Delta at No. 5, ASA at No. 6 and Comair at No. 12.

Among the nation's major airports, Hartsfield-Jackson International Airport came in at No. 9 for on-time departures with 85.3 percent of flights departing on time, up from No. 12 a year earlier. For on-time arrivals, the Atlanta airport ranked No. 6 in May with 84.3 percent of flights arriving on time, down from No. 5 a year earlier.