CALGARY — WestJet pilots are again seeking to form a union, the Air Line Pilots Association, International said Thursday.

It says pilots at the Calgary-based airline filed membership cards with the Canada Industrial Relations Board to hold a vote to be represented by the world’s largest airline pilot union.

The association says it expects a secret-ballot election will be held in May after the board verifies the membership cards.

WestJet pilots voted to reject a unionization drive by the WestJet Professional Pilots Association in 2015.

ALPA president Capt. Tim Canoll said in a news release that a vote to join the union will give the pilots the resources to begin negotiations for a collective bargaining agreement.

WestJet didn’t immediately respond to a request for comment.

The Air Line Pilots Association represents 55,000 pilots at 32 airlines in Canada and the U.S., including Air Transat, Air Georgian, Bearskin, Calm Air and Jazz Aviation.