HEBRON, Ky. (AP) -- Comair, the nation's second-largest regional airline, said Wednesday it will begin canceling some flights in preparation for a potential strike by its pilots' union.

"We want to reach an agreement as quickly as possible and we are diligently working toward that goal," said Comair spokeswoman Meghan Glynn. "But we also must take some precautions in the best interest of our customers and employees."

Comair pilots have rejected the company's five-year contract offer and could go on strike as early as 12:01 a.m. Monday if no agreement is reached. The date marks the end of a 30-day cooling-off period.

Comair officials said Wednesday that changes in the flight schedule would begin Thursday. Mediated talks between Comair and the Air Line Pilots Association are to resume Friday in Washington.

Comair has said that if no agreement is reached and pilots walk out, it would suspend all flight operations but would keep about 4,000 other employees on the job.

Union spokesman Paul Lackie was not surprised by Comair's decision to cancel some flights.

"I think it's safe to say that they are putting more energy into planning for a strike than in reaching agreement," he said.

Glynn said the company is contacting affected customers individually in advance of any flight changes. Comair is advising customers to make sure their travel reservations include telephone contacts in their departure and arrival cities.

Comair said it would try to minimize disruption of travel plans by providing customers with alternate transportation on Delta, Delta Express, Delta Connection or other airlines. Comair also has issued some tips for customers on its website.

Comair's has 323 daily flights at Cincinnati/Northern Kentucky International Airport, where it is based. Its parent company, Delta Air Lines, has 182 flights from the same airport. Together, the companies account for 90 percent of the airport's flights.

Comair, which also has a hub in Orlando, Fla., has flights to 95 cities in the United States, Canada, Mexico and the Bahamas. It serves more than 8 million passengers annually.

The airline services Charleston, W.Va., and has announced plans to provide service to Bridgeport, W.Va.

Delta and its pilots, who also have been involved in contract negotiations, said Wednesday that they had reached tentative agreements on travel expenses, leaves of absence and miscellaneous items.

Some major issues still to be resolved include salary, retirement benefits, back pay and the contract's length.

Delta also said Wednesday that it is confident of Comair's ability to work toward a settlement with its pilots and would not intervene in the Comair talks.