The Northwest Airlines pilots union says a shortage of pilots is to blame for a recent flurry of cancellations across the country.

Northwest Airlines canceled 332 flights Sunday and Monday, cancellations that Northwest spokesman Dean Breest blames on severe weather.

“The recent severe weather events have caused Northwest Airlines to experience some crew shortages,” Breest said in a statement. “Northwest apologizes for any inconvenience incurred as the airline continues to recover from these recent weather events.”

Pilots union spokesman Monty Montgomery says pilots have reached contractual limits as to the number of hours they can fly.

“It’s a staffing issue,” said Montgomery, who says cancellations could be as high as 450 since Saturday. “Our pilots are operating at contractual limits. The summer flying season is in full swing and we are operating at our max.”