CHICAGO - United Airlines canceled at least 120 flights at O'Hare International Airport on Sunday, and the company blamed the cancellations on pilots who have refused to worked overtime since their contract expired in April.
On Saturday, 150 flights at O'Hare, more than 15 percent of the total, were scrapped for the same reason.
A line of thunderstorms in the central United States Sunday evening also created delays of up to two hours , said city Aviation Department spokeswoman Monique Bond.
United spokesman Chris Brathwaite said many of the airline's pilots had already worked all their allotted weekly hours trying to make up for flights canceled Thursday and Friday because of bad weather in the East.
The weekend cancellations involved flights to and from locations all over the country.
Since spring, United has had cancel or delay scores of flights because of pilot shortages, and Brathwaite couldn't say when the continuing problem would be resolved.
''Hopefully soon,'' he said.
United has about 960 flights per day at O'Hare.
United and the pilots' union are negotiating a contract with a federal mediator and hope to have a new agreement in place by early September.
A spokesman for the union, the Air Line Pilots Association, did not immediately return a call for comment Sunday. In the past, the union has denied there is an organized effort to refuse overtime work. The union represents more than 58,000 pilots at 50 airlines in the United States and Canada.
On the Net:
Air Line Pilots Association: http://www.alpa.org