WestJet Airlines must change its hiring strategy for the company's new bargain carrier, Swoop, an Air Line Pilots Association executive said on Tuesday, citing a recent Canadian labour board order.

The country's second-largest carrier can no longer recruit its pilots through two-year leaves of absence to fly for Swoop and will have to rescind any existing offers, Rob McFadyen, chairman of WestJet's ALPA master executive council, said in a telephone interview.

ALPA, which is negotiating its first contract with Calgary-based WestJet, said the carrier was trying to bypass the union by luring its own pilots to fly for Swoop under different working conditions. It was not immediately clear what conditions the pilots were being offered to fly for Swoop.

ALPA had argued that pilots who work for the new no-frills carrier should have the same working conditions as those who fly WestJet planes, with the union arguing they should all have the same contract.

In its March 2 order, seen by Reuters, the Canada Industrial Relations Board, or CIRB, told WestJet to "rescind the offer of a two-year leave of absence policy ... in order to fly for Swoop."

The decision risks complicating expansion plans by Calgary-based WestJet, which is growing its international network while launching the no-frills carrier in June, raising analyst concerns.

WestJet spokeswoman Lauren Stewart said by email that Swoop's launch remained on track and that the carrier "remains committed to engaging in constructive dialogue with" the pilots' union.

AltaCorp analyst Chris Murray said by email that it was still too early to determine the "impact this could have on timing or costs, but certainly continues to add to the complexity."