Air Canada had planned to resume operations of Air Canada and Air Canada Rouge flights on Sunday after those flights were grounded on Saturday due to the labour disruption, but the airline said it was not able to resume operations due to “CUPE leadership’s unlawful strike activities.”

While Air Canada says it would not negotiate with the union until flight attendants return to work, CUPE says the two sides were in discussions Monday night with a mediator.

If you've been following the Air Canada strike throughout its twists and turns, you've likely heard the term "ground pay," or noticed flight attendants holding signs decrying unpaid labour. But what is that unpaid work?