United Airlines cancels more flights CHICAGO, Aug. 7 - United Airlines canceled over 160 flights Monday as weather woes and labor problems continued to cause headaches for travelers.

The cancellation of hundreds of flights over the weekend at O'Hare International Airport led to overcrowding on Monday flights, said Chicago Department of Aviation spokeswoman Monique Bond.

Additional cancellations throughout the United system Monday continued to plague weary travelers already stranded at airports around the country.

United spokesman Matt Triaca said 165 flights out of the 2,400 scheduled were canceled.

VIDEO: United cancels 160 flights

Triaca blamed weather and strained air traffic control towers for the delays and cancellations. United is affected by weather much more than other airlines because of the location of its hubs, he said.

"A flight out of O'Hare may be canceled due to weather in the east. If the crew and the plane are out of position, that plane can't fly," he said.

Triaca said strained air traffic control towers at many airports also add to the problem with not enough gates and crowded air space.

Triaca said a small percentage of flights were canceled because of contract negotiations with United pilots. They have refused to work overtime since their contract expired in April.

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. Triaca said there have been positive developments in the negotiations, but he would not elaborate.

The airline has cut back on the number of flights this summer, reducing its flight load from May through September.

Triaca says it's an effort to reduce the number of flights pilots have to fly.