Continental Airlines canceled 24 flights on Wednesday due to a shortage of pilots after a barrage of sick calls, according to the carrier's parent, United Continental Holdings Inc.

Airline spokeswoman Megan McCarthy said most of the cancellations were flights from Newark, New Jersey. The airline was working to book the affected passengers on other flights, she said.

The incident may spotlight a staffing shortage at the airline, or possibly pilot discontent with management over the slow pace of labor talks.

"It's a legitimate question as to whether this is some kind of a work-to-rule or slow-down," said Robert Mann, an airline consultant at R.W. Mann & Co.

"It would be equally appropriate to question the company and whether or not it has sufficient manning toward the end of a summer month when weather may have claimed pilot time earlier in the month," he said, referring to limits on the number of hours a pilot can legally fly each month.

United Continental was formed last year from the merger of United Airlines and Continental Airlines.

The company is currently negotiating a joint contract with the pilots, who have voiced impatience over the slow pace of the talks.

McCarthy declined to say if the sick calls were an orchestrated work action similar to a labor strike. Strikes by airline employees are restricted by the U.S. Railway Labor Act, which safeguards interstate commerce.

Amy Flanagan, a spokesperson for the Air Line Pilots Association union, which represents the Continental pilots, declined to comment on the sick calls.

When asked directly if the calls were a planned effort by workers to disrupt flights, Flanagan declined to confirm or deny it.

On a conference call last week with analysts and reporters, United Continental Chief Executive Jeff Smisek said he did not know if a pilot contract would be reached this year.

"The target remains to get a deal done as promptly as I can," Smisek said. "I would love to get a deal done with our pilots by the end of this year. I don't know whether we will be able to do that. It does take two to tango."

United Continental's shares were down 3.6 percent at US$18.08 in afternoon trading.