Air Canada offered its flight attendants an overall increase of more than 30% over four years ahead of a potential strike, according to a person familiar with the negotiations.

Air Canada flight attendants want to make gains on unpaid work that go beyond recent advances secured by their U.S. counterparts, a union leader said on Wednesday, in a fresh test of the way airlines compensate cabin crews.

The Canadian Union of Public Employees’ (CUPE) Air Canada component said over 99 per cent of Air Canada flight attendants voted to strike, adding that the vote result reflects its members’ “deep frustration” after months of stalled negotiations toward a new contract.