WestJet has sent layoff notices to 1,700 of its pilots amid an unprecedented reduction in air travel due to the global COVID-19 pandemic.

The Calgary-based airline said the layoffs affect pilots with WestJet, WestJet Encore and Swoop, and will take effect either May 1 or June 1.

In an emailed statement, a spokesperson said the move was a last resort, but noted the pandemic has had a "colossal" impact on the airline industry.

"These notifications are in response to the COVID-19 global crisis that is shutting borders, encouraging only essential travel and forcing a dramatic reduction in flying that has led to the grounding of almost three-quarters of the WestJet fleet," the statement said.

"Issuing layoffs, in response to this crisis, has always been a last resort for WestJet; however, the impact of COVID-19 on the aviation industry is colossal, and WestJet is making difficult but necessary decisions to right-size our airline to weather the crisis. These actions will play a crucial part in WestJet's ability to recover quickly and participate in Canada's economic recovery."

The Air Line Pilots Association, the union representing the pilots, said in a statement emailed to CBC News that its "negotiation goal is to arrive at an appropriate balance between short-term economic accommodations and protecting the value of the jobs remaining."

The ALPA said it will continue to negotiate with WestJet to protect its members' interests while preserving as many pilot positions as possible.

WestJet said it is participating in the Canadian Emergency Wage Subsidy (CEWS) program and said the pilots will be placed on an inactive status and will remain on payroll while the program is in effect.

In March, WestJet announced it was cutting roughly half of its 14,000 employees with the elimination of 6,900 positions. But it said last week it would rehire nearly 6,400 of those workers with the help of a federal wage subsidy.

It has also suspended international flights until at least May.